Fix fuzzy matching edge cases for 6.0.1

[ycherkes]

Summary

• Fix near-perfect and empty-input PartialRatio behavior.
• Make cached WeightedRatio equivalent to uncached scoring.
• Correctly dispose cached token-sort resources.
• Validate ExtractTop limits across sequential, cached, parallel, and pipeline
  APIs.
• Make default preprocessing culture-invariant.
• Update documentation, changelog, and version metadata to 6.0.1.

Verification

• NET8.0: 5,138 tests passed.
• NET10.0: full test suite passed.