introduce a type for stateless reset tokens

[marten-seemann]

Also, pass around the [16]byte by value rather than by pointer. Turns out that's actually faster, and it makes the code a bit cleaner.

[codecov]

Codecov Report

Merging #2668 into master will decrease coverage by 0.16%.
The diff coverage is 92.00%.

@@            Coverage Diff             @@
##           master    #2668      +/-   ##
==========================================
- Coverage   86.62%   86.46%   -0.16%     
==========================================
  Files         123      122       -1     
  Lines        9778     9764      -14     
==========================================
- Hits         8470     8442      -28     
- Misses        973      988      +15     
+ Partials      335      334       -1     

Impacted Files	Coverage Δ
conn_id_generator.go	90.00% <ø> (-0.32%)	⬇️
internal/protocol/protocol.go	100.00% <ø> (ø)
internal/wire/new_connection_id_frame.go	95.12% <ø> (ø)
server.go	84.57% <ø> (+0.89%)	⬆️
session.go	76.92% <85.71%> (-0.19%)	⬇️
packet_handler_map.go	78.47% <88.89%> (-0.10%)	⬇️
conn_id_manager.go	94.17% <100.00%> (ø)
internal/wire/transport_parameters.go	89.72% <100.00%> (ø)
qlog/event.go	95.98% <100.00%> (ø)
qlog/qlog.go	95.37% <100.00%> (+0.02%)	⬆️
... and 9 more

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