fix(subpath): correct exports type cast; add fast-check fuzz harness

[the-simian]

Two changes on the test surface plus a housekeeping biome update.

Test code

• test/subpathExports.test.ts:190 — change Object.entries<Record<string, string>> to Object.entries<{ import: string; types: string }>. The loop body reads .import and .types; the original cast lied about the shape. No runtime behavior change.
• test/fuzz.test.ts (new) — add a fast-check property test asserting rgbToRgba throws only Error instances across 1000 arbitrary string inputs per run. Adds fast-check@4.7.0 as a devDep. Credits OpenSSF Scorecard's Fuzzing check (currently 0/10; will flip on next scan).

Tooling

• Bump @biomejs/biome 2.4.12 → 2.4.13; bunx biome migrate --write (schema URL only); reformat the widened Object.entries call to respect the configured line width.

Test results

472/472 passing (was 471); fuzz test runs in ~40ms. Full suite under 200ms. Coverage held at 100%.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (4306543) to head (9e66cfd).
⚠️ Report is 6 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main       #20   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           30        30           
  Lines         9839      9839           
=========================================
  Hits          9839      9839           

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