enhancement(license-detection): cache PositionSet on LicenseMatch to avoid redundant BitSet construction in filter passes

[abraemer]

Summary

LicenseMatch stores PositionSpan (lightweight range/discrete enum), but PositionSet (BitSet for O(1) membership) is constructed on-demand via qspan_set() / ispan_set() each time containment/overlap is checked in filter passes. When the same match is checked against many others during merge/overlap filtering, the BitSet is reconstructed repeatedly.

Proposal

Either cache the PositionSet on LicenseMatch after first construction, or construct all position sets once at the start of a filter pass and pass them through.

Benefits

• Eliminates redundant BitSet construction in hot filter loops
• BitSet's O(1) membership tests only pay off when amortized over many queries
• Particularly impactful for the merge and overlap filter stages which do many pairwise comparisons

When

When profiling shows filter-pass time is significant, or when the filter pipeline is next restructured.