Invalidate stale rule caches missing bytes_prefix_index

[itxsamad1]

Summary

Fixes runtime crashes when loading stale rule caches whose pickled _RuleFeatureIndex objects predate the bytes_prefix_index field (#2961).

• Bump on-disk cache format version from v1 to v2 (invalidates old cache files at load time)
• Validate cached rulesets after unpickling and treat outdated schemas as cache misses
• Broaden load error handling to delete corrupt cache files instead of crashing later during matching

Fixes #2961

Test plan

• pytest tests/test_rule_cache.py (5 passed)
• Added test_ruleset_cache_rejects_outdated_schema simulating pre-bytes_prefix_index index objects

[github-actions]

Please add bug fixes, new features, breaking changes and anything else you think is worthwhile mentioning to the master (unreleased) section of CHANGELOG.md. If no CHANGELOG update is needed add the following to the PR description: [x] No CHANGELOG update needed

[gemini-code-assist]

Code Review

This pull request updates the rule cache mechanism to handle outdated internal schemas by incrementing the cache version, expanding exception handling during cache loading, and introducing a validation check to ensure the cached ruleset contains the required attributes. Feedback suggests safely accessing the _feature_indexes_by_scopes attribute using getattr to prevent potential AttributeError crashes, as this check is performed outside the main try-except block.

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[gemini-code-assist]

If the unpickled ruleset is from an older cache version or is corrupted, it might not have the _feature_indexes_by_scopes attribute. Accessing it directly will raise an AttributeError and crash the application, as this call is outside the try-except block in load_cached_ruleset. Using getattr to safely retrieve the attribute prevents potential crashes.

Suggested change

	for feature_index in ruleset._feature_indexes_by_scopes.values():
	if not hasattr(feature_index, "bytes_prefix_index"):
	return False
	feature_indexes = getattr(ruleset, "_feature_indexes_by_scopes", None)
	if feature_indexes is None:
	return False
	for feature_index in feature_indexes.values():
	if not hasattr(feature_index, "bytes_prefix_index"):
	return False

[williballenthin]

@itxsamad1 would you please explain the sequence of events that led to you encountering this issue? i'm surprised that the caching logic doesn't already notice this.