Fix no-bigint build failures, check those in CI

[fasterthanlime]

I forgot to fix a couple lines in the last PR — now they're checked by pre-commit, before committing (I'm assuming?) and in CI.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.55%. Comparing base (b09b969) to head (ac903d0).
Report is 4 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #138   +/-   ##
=======================================
  Coverage   94.55%   94.55%           
=======================================
  Files          12       12           
  Lines        2040     2040           
=======================================
  Hits         1929     1929           
  Misses        111      111           

Files with missing lines	Coverage Δ
crates/jiter/src/value.rs	94.10% <ø> (ø)

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[codspeed-hq]

CodSpeed Performance Report

Merging #138 will degrade performances by 10.99%

_{Comparing bearcove:bigint-check (ac903d0) with main (b09b969)}

Summary

❌ 1 regressions
✅ 72 untouched benchmarks

⚠️ Please fix the performance issues or acknowledge them on CodSpeed.

Benchmarks breakdown

	Benchmark	main	bearcove:bigint-check	Change
❌	sentence_jiter_value	7.9 µs	8.9 µs	-10.99%

[fasterthanlime]

CI failure is unrelated and perf regression is.. unexplainable. Oh well.

[davidhewitt]

LGTM, the perf regression seems to be just variance caused by allocations.