quic: serialize stream reset code as string

[manNomi]

Description

QuicStreamState.toJSON() returned resetCode as a BigInt.
QuicStreamState.toString() serializes that object with
JSONStringify(), so serializing a live stream state threw
TypeError: Do not know how to serialize a BigInt. Calling
JSON.stringify() on the state failed for the same reason.

Serialize resetCode as a string, matching the handling of other 64-bit
QUIC state values. Using a string also preserves values outside JavaScript's
safe integer range. This only changes the JSON representation; it does not
change QUIC stream reset processing or the stored reset code.

Add a regression assertion that serializes a stream state and verifies the
parsed resetCode value.

[nodejs-github-bot]

Review requested:

• @nodejs/quic

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.24%. Comparing base (fb5d01f) to head (83661c1).

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #64577      +/-   ##
==========================================
- Coverage   90.24%   90.24%   -0.01%     
==========================================
  Files         739      739              
  Lines      241772   241772              
  Branches    45561    45557       -4     
==========================================
- Hits       218194   218182      -12     
- Misses      15111    15115       +4     
- Partials     8467     8475       +8     

Files with missing lines	Coverage Δ
lib/internal/quic/state.js	100.00% <100.00%> (ø)

... and 35 files with indirect coverage changes

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