fix: check sparse-array holes in the isArrayOf type guard

[gjbkz]

Requested by Kei · project thread

Before: isArrayOf(isString)(new Array(1)) returned true, narrowing a sparse array to string[], while validate() and validateAll() rejected the same input at path [0].

After: holes are checked as undefined on every path, so the guard, test(), validate() and validateAll() agree. A hole fails isArrayOf(isString) and passes isArrayOf(isOptionalOf(isString)).

How: the boolean path now uses Array.prototype.findIndex(), which visits holes as undefined, instead of every(), which skips them. An earlier explicit index loop pushed the minified UUID bundle over the 5916-byte budget in test/package.test.ts (5924 bytes) once #453 and #454 were merged; with findIndex() it is 5877 bytes. Tests cover empty, fully sparse, mixed, explicit-undefined and dense arrays against both checkers; the test fails on main and passes here.

Closes #450

🤖 Generated with Claude Code

https://claude.ai/code/session_019BJENnU8SXcDH2Tcx5EWE4

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.46%. Comparing base (bcc1d53) to head (bba1742).
⚠️ Report is 4 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #455   +/-   ##
=======================================
  Coverage   98.46%   98.46%           
=======================================
  Files          52       52           
  Lines        3055     3057    +2     
  Branches      327      327           
=======================================
+ Hits         3008     3010    +2     
  Misses         46       46           
  Partials        1        1           

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[gjbkz]

Reviewed commit 43904af416b277c018477dd4e4af80d33f85cd2c. No actionable issues found in this change.

Visiting each array index aligns the boolean guard with diagnostic traversal: holes are checked as undefined. The regression coverage checks empty, fully sparse, mixed, explicit-undefined, and dense arrays with both string and optional-string element checkers across the boolean, test(), validate(), and validateAll() paths.

Validation: the complete source unit-test suite passed locally on this reviewed version, and the GitHub Actions test workflow for this commit completed successfully. The latest head is unchanged from the locally tested version.