Stop state pseudo-classes from re-entering the engine - #178

@jdalton The key part of the solution I proposed was the elimination of the need to use a call to the matches function to detect if it is a native function or not. This heads off future bugs like this.

Current fix

This PR now preserves matcher replacement and LEGACY changes. An unchanged delegating matcher is cached per document, with a fast path for consecutive queries. Changing the selected function clears its delegation result; changing LEGACY clears mode-dependent document records.

The related uninstall and autofill defects are tracked separately in #195 and #196.

@jdalton Your code makes calls repeatedly on every use to a function to detect if it is native or not native. This wastes cpu cycles and is prone to create future bugs.

The cache optimization now preserves live matcher replacement and LEGACY changes. It reuses delegation results only while the selected matcher remains unchanged. Standard matcher reads remain necessary to observe host changes; prefixed aliases are cached only in legacy mode.

The two later audit regressions are covered by unit tests and local browser regressions using the upstream WPT harness. The full local CI workflow passes without lowering coverage thresholds. See the current explanation for compatibility details and the related fixes in #195 and #196.

The merge audit found two compatibility gaps, so I am leaving this open.

• An element-level matcher can change after an unsupported-selector exception. The regression on current master returns false and then true after replacing node.matches; this branch returns false twice because it reads the prototype instead.
• With standard matches absent and a working prefixed matcher, querying in modern mode and then enabling LEGACY still returns false. The cached document record is not refreshed when the mode changes.

Both were reproduced against this PR head, 5ff4409, and compared with current master. The new native-reentry tests on master also cover the first behavior. The existing reentry guard has already removed the stack-exhaustion problem; this cache optimization needs to preserve host behavior and invalidate mode-dependent records before it can merge.

Both audit regressions are fixed and covered. The repaired PR passed the complete local Docker workflow and GitHub CI on top of merged #195, and is now merged. Issues #171, #172, and #177 are resolved in source; this does not indicate a new npm release. The related autofill fix continues in #196.