Direct conversion from u8 to Opcode

[HalidOdat]

Optimizes opcode fetching by removing the checks that validate if it's a correct opcode. every u8 combination matches to a valid Opcode variant (even if it's reserved).

Main:

Richards: 20.5
DeltaBlue: 24.8
RayTrace: 81.0
----
Score (version 7): 34.5
undefined

PR:

Richards: 20.6
DeltaBlue: 24.8
RayTrace: 82.1
----
Score (version 7): 34.8
undefined

There is a small improvement in performance.

[github-actions]

Test262 conformance changes

Test result	main count	PR count	difference
Total	94,118	94,118	0
Passed	74,620	74,620	0
Ignored	17,750	17,750	0
Failed	1,748	1,748	0
Panics	0	0	0
Conformance	79.28%	79.28%	0.00%

[codecov]

Codecov Report

Merging #2951 (e0b97c4) into main (44ef49e) will increase coverage by 0.34%.
The diff coverage is 66.66%.

❗ Current head e0b97c4 differs from pull request most recent head bb4d02f. Consider uploading reports for the commit bb4d02f to get more accurate results

@@            Coverage Diff             @@
##             main    #2951      +/-   ##
==========================================
+ Coverage   50.05%   50.40%   +0.34%     
==========================================
  Files         446      444       -2     
  Lines       45975    45355     -620     
==========================================
- Hits        23015    22859     -156     
+ Misses      22960    22496     -464     

Impacted Files	Coverage Δ
boa_engine/src/vm/code_block.rs	55.80% <0.00%> (-0.51%)	⬇️
boa_engine/src/vm/flowgraph/mod.rs	0.00% <0.00%> (ø)
boa_engine/src/vm/opcode/nop/mod.rs	0.00% <ø> (ø)
boa_engine/src/vm/opcode/mod.rs	53.33% <80.00%> (+7.87%)	⬆️
boa_engine/src/vm/mod.rs	54.16% <100.00%> (+0.27%)	⬆️

... and 80 files with indirect coverage changes

[jasonwilliams]

LGTM

[raskad]

I think we don't need transmute here to get the performance improvement. Even on opt-level 1 the produced code is the same when all u8s are matched to their enum variants: https://rust.godbolt.org/z/oxMeMMrjG.

We should also remove the Opcode::from_raw function since that can be done with into() safeley now.

[raskad]

Looks good