[feature] Improve afring throughput using code optimization

[fako1024]

@els0r Things done here:

• Instead of performing individual calls / casts via unsafe for all data fields, the portion of the TPacketHeaderV3 struct is cast directly (memory-aligned) and then worked with locally
• Compiler inlining is optimized (in the sense that functions are either guaranteed to be inlined by the compiler or they are manually inlined at the expense of a little bit of code duplication on the innermost layers)
• Complete restructuring of the core PPOLL loop and handling to focus on fast path (non-poll extraction from current active block) while improving code readability
• Some micro-optimizations to assembly code
• Significant improvements to reproducibility of benchmarks (by means of minimizing scheduler overhead when handling goroutines)
• Fix NextPayloadInPlace to actually do what it's supposed to (instead of performing a zero-copy operation, which is why performance is "worse")
• Some minor code cleanup

Benchmarks (on three different systems) further below. The improvements for the non-zero-copy cases are nice to have, but they mostly serve as a consistency check that the performed changes are beneficial across the board (and that no regressions are introduced). Most important are the improvements for the ZeroCopy methods, which are in the range of 12-17% (depending on system), which, given the level of optimization we're looking at, is quite a lot:

cpu: Intel(R) Core(TM) i3-2100T CPU @ 2.50GHz
CaptureMethods/NextPacket_10485kiBx4-4             103.4n ± 1%   103.3n ± 1%        ~ (p=0.735 n=50)
CaptureMethods/NextPacketInPlace_10485kiBx4-4      40.20n ± 1%   39.94n ± 1%   -0.67% (p=0.043 n=50)
CaptureMethods/NextPayload_10485kiBx4-4            91.19n ± 1%   88.76n ± 1%   -2.66% (p=0.000 n=50)
CaptureMethods/NextPayloadInPlace_10485kiBx4-4     21.56n ± 1%   32.90n ± 3%  +52.57% (p=0.000 n=50)
CaptureMethods/NextPayloadZeroCopy_10485kiBx4-4    19.73n ± 1%   16.38n ± 0%  -16.98% (n=50)
CaptureMethods/NextIPPacket_10485kiBx4-4           91.75n ± 1%   89.80n ± 1%   -2.14% (p=0.000 n=50)
CaptureMethods/NextIPPacketInPlace_10485kiBx4-4    33.33n ± 2%   33.51n ± 2%        ~ (p=0.945 n=50)
CaptureMethods/NextIPPacketZeroCopy_10485kiBx4-4   19.75n ± 1%   16.68n ± 0%  -15.59% (n=50)
CaptureMethods/NextPacketFn_10485kiBx4-4           20.70n ± 1%   19.52n ± 1%   -5.72% (n=50)
CaptureMethods/NextPacket_10kiBx512-4              211.2n ± 1%   214.0n ± 1%   +1.35% (p=0.046 n=50)
CaptureMethods/NextPacketInPlace_10kiBx512-4       210.8n ± 4%   197.1n ± 2%   -6.48% (p=0.000 n=50)
CaptureMethods/NextPayload_10kiBx512-4             190.8n ± 2%   182.6n ± 1%   -4.32% (p=0.000 n=50)
CaptureMethods/NextPayloadInPlace_10kiBx512-4      200.4n ± 2%   195.5n ± 1%        ~ (p=0.058 n=50)
CaptureMethods/NextPayloadZeroCopy_10kiBx512-4     200.8n ± 2%   189.8n ± 2%   -5.48% (p=0.000 n=50)
CaptureMethods/NextIPPacket_10kiBx512-4            189.4n ± 1%   180.1n ± 1%   -4.91% (p=0.000 n=50)
CaptureMethods/NextIPPacketInPlace_10kiBx512-4     203.0n ± 2%   192.9n ± 2%   -4.98% (p=0.000 n=50)
CaptureMethods/NextIPPacketZeroCopy_10kiBx512-4    199.6n ± 2%   177.3n ± 2%  -11.20% (n=50)
CaptureMethods/NextPacketFn_10kiBx512-4            199.1n ± 2%   198.8n ± 4%        ~ (p=0.168 n=50)

cpu: Intel(R) Celeron(R) N5105 @ 2.00GHz
CaptureMethods/NextPacket_10485kiBx4-4             80.36n ± 0%   79.39n ± 0%   -1.20% (p=0.000 n=50)
CaptureMethods/NextPacketInPlace_10485kiBx4-4      37.06n ± 1%   34.04n ± 1%   -8.16% (p=0.000 n=50)
CaptureMethods/NextPayload_10485kiBx4-4            74.45n ± 0%   68.41n ± 1%   -8.12% (n=50)
CaptureMethods/NextPayloadInPlace_10485kiBx4-4     20.16n ± 0%   29.77n ± 0%  +47.69% (p=0.000 n=50)
CaptureMethods/NextPayloadZeroCopy_10485kiBx4-4    18.32n ± 1%   15.91n ± 0%  -13.15% (n=50)
CaptureMethods/NextIPPacket_10485kiBx4-4           71.47n ± 0%   70.93n ± 0%   -0.75% (p=0.000 n=50)
CaptureMethods/NextIPPacketInPlace_10485kiBx4-4    31.10n ± 1%   31.86n ± 1%   +2.46% (p=0.002 n=50)
CaptureMethods/NextIPPacketZeroCopy_10485kiBx4-4   18.25n ± 0%   16.15n ± 0%  -11.51% (n=50)
CaptureMethods/NextPacketFn_10485kiBx4-4           19.24n ± 0%   21.73n ± 9%        ~ (p=0.051 n=50)
CaptureMethods/NextPacket_10kiBx512-4              128.6n ± 1%   129.5n ± 2%        ~ (p=0.934 n=50)
CaptureMethods/NextPacketInPlace_10kiBx512-4       124.3n ± 0%   122.0n ± 1%   -1.85% (p=0.000 n=50)
CaptureMethods/NextPayload_10kiBx512-4             126.7n ± 1%   122.6n ± 1%   -3.27% (p=0.000 n=50)
CaptureMethods/NextPayloadInPlace_10kiBx512-4      128.9n ± 1%   122.0n ± 1%   -5.39% (p=0.000 n=50)
CaptureMethods/NextPayloadZeroCopy_10kiBx512-4     130.0n ± 1%   126.8n ± 1%   -2.42% (p=0.000 n=50)
CaptureMethods/NextIPPacket_10kiBx512-4            125.0n ± 1%   122.9n ± 1%   -1.64% (p=0.000 n=50)
CaptureMethods/NextIPPacketInPlace_10kiBx512-4     125.0n ± 1%   122.0n ± 1%   -2.44% (p=0.000 n=50)
CaptureMethods/NextIPPacketZeroCopy_10kiBx512-4    129.3n ± 1%   127.3n ± 1%   -1.55% (p=0.000 n=50)
CaptureMethods/NextPacketFn_10kiBx512-4            129.7n ± 1%   124.9n ± 1%   -3.74% (p=0.000 n=50)

cpu: Intel(R) Core(TM) i7-10510U CPU @ 1.80GHz
CaptureMethods/NextPacket_10485kiBx4-4             54.54n ± 0%   53.58n ± 0%   -1.75% (p=0.000 n=50)
CaptureMethods/NextPacketInPlace_10485kiBx4-4      22.50n ± 1%   22.33n ± 0%   -0.78% (p=0.002 n=50)
CaptureMethods/NextPayload_10485kiBx4-4            48.56n ± 0%   47.34n ± 0%   -2.50% (p=0.000 n=50)
CaptureMethods/NextPayloadInPlace_10485kiBx4-4     13.76n ± 0%   18.67n ± 6%  +35.68% (p=0.000 n=50)
CaptureMethods/NextPayloadZeroCopy_10485kiBx4-4    12.89n ± 0%   11.16n ± 0%  -13.42% (n=50)
CaptureMethods/NextIPPacket_10485kiBx4-4           48.20n ± 0%   47.38n ± 0%   -1.70% (p=0.000 n=50)
CaptureMethods/NextIPPacketInPlace_10485kiBx4-4    19.24n ± 3%   19.57n ± 0%        ~ (p=0.422 n=50)
CaptureMethods/NextIPPacketZeroCopy_10485kiBx4-4   12.84n ± 0%   11.19n ± 0%  -12.85% (n=50)
CaptureMethods/NextPacketFn_10485kiBx4-4           13.40n ± 0%   12.86n ± 0%   -4.03% (n=50)
CaptureMethods/NextPacket_10kiBx512-4              138.4n ± 3%   132.4n ± 2%        ~ (p=0.361 n=50)
CaptureMethods/NextPacketInPlace_10kiBx512-4       155.6n ± 6%   165.1n ± 2%   +6.14% (p=0.010 n=50)
CaptureMethods/NextPayload_10kiBx512-4             149.4n ± 7%   150.7n ± 2%   +0.87% (p=0.016 n=50)
CaptureMethods/NextPayloadInPlace_10kiBx512-4      173.9n ± 5%   165.2n ± 3%        ~ (p=0.622 n=50)
CaptureMethods/NextPayloadZeroCopy_10kiBx512-4     167.4n ± 6%   167.4n ± 4%        ~ (p=0.051 n=50)
CaptureMethods/NextIPPacket_10kiBx512-4            151.2n ± 3%   151.4n ± 4%        ~ (p=0.136 n=50)
CaptureMethods/NextIPPacketInPlace_10kiBx512-4     157.9n ± 5%   162.4n ± 2%   +2.82% (p=0.034 n=50)
CaptureMethods/NextIPPacketZeroCopy_10kiBx512-4    163.1n ± 6%   171.5n ± 3%   +5.12% (p=0.003 n=50)
CaptureMethods/NextPacketFn_10kiBx512-4            168.6n ± 4%   167.1n ± 4%        ~ (p=0.480 n=50)

Closes #71