fix: correct length-coded number size for the 3-byte range

[lazerg]

Packet.lengthCodedNumberLength() returns 5 for the 0xffff <= n < 0xffffff range, but writeLengthCodedNumber() only ever writes 4 bytes there (a 1-byte 0xfd marker plus a 3-byte Int24). Before #4494, packet sizes were measured with a real dry-run write, so this drift never surfaced. Since #4494 switched to computing sizes arithmetically from lengthCodedNumberLength(), any string/JSON/blob parameter whose encoded length falls in that range now throws COM_STMT_EXECUTE serialized N bytes, expected N+1. This fixes the length function to match what the writer actually emits.

Fixes #4499

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.53%. Comparing base (ca10232) to head (7b6ac9e).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #4500   +/-   ##
=======================================
  Coverage   92.53%   92.53%           
=======================================
  Files          93       93           
  Lines       15972    15972           
  Branches     2290     2290           
=======================================
  Hits        14780    14780           
  Misses       1192     1192           

Flag	Coverage Δ
compression-0	92.15% <100.00%> (ø)
compression-1	92.51% <100.00%> (ø)
static-parser-0	91.35% <100.00%> (ø)
static-parser-1	91.47% <100.00%> (ø)
tls-0	92.10% <100.00%> (ø)
tls-1	92.53% <100.00%> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[sidorares]

Thanks @lazerg ! Fix looks solid, thanks for catching the bug (which existed for long time, but recent change accidentally uncovered it). I added some integration tests in #4503

[sidorares]

@lazerg fix published as mysql@3.24.2