fix: skip sparse array holes in optimized filter

[xianjianlf2]

With enableArrayMethods(), filtering a sparse array calls the predicate for empty slots. For example, produce(new Array(3), draft => draft.filter(() => true)) returns three undefined values instead of []; a predicate that reads an object property can also throw on a hole.

Check whether each index exists before invoking the predicate, matching native filter. Explicit undefined elements are still visited, and selected objects remain drafts whose mutations update the original positions.

The tests run with the plugin and auto-freezing independently enabled and disabled. Four cases fail before the fix. On Node 24.18.0, yarn test passes: 3,844 source tests and 3,293 production-build tests, with eight existing skips in each suite; the build and Flow checks pass. Prettier and git diff --check also pass.

Prepared with AI assistance, including code and regression tests.