WIP: calculate line/chunk hotness

[bartveneman]

New output fields:

• chunk.coverage_count: number — how many input Coverage objects covered that chunk (0 = uncovered, 1+ = covered N times)
  = chunk.is_covered: boolean — unchanged, backward-compatible (= coverage_count > 0)
  = result.max_coverage_count: number — highest count across all chunks in a stylesheet/result

Files changed:

• decuplicate.ts — new WeightedRange/WeightedCoverage types + sweep-line algorithm that counts overlapping ranges, then merges adjacent same-count segments (preserving the old 1-byte tolerance)
• extend-ranges.ts — made generic so it works with both plain and weighted ranges
• chunkify.ts — coverage_count added to Chunk; adjacent covered chunks merge keeping the max count (needed to keep line counts stable when the same stylesheet is loaded multiple times)
• index.ts — threads WeightedCoverage through the pipeline; computes max_coverage_count in stats

Design note: Adjacent covered chunks with different counts are merged keeping the max count. This is intentional — it preserves correct line counts when the same stylesheet is covered in overlapping but not identical ways across multiple sessions.

---

some issues still preventing me from merging this:

1. When a large chunk that was covered once contains a chunk that was covered 10 times, the whole large chunk gets marked with 10 hits. Meh.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 98.52941% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 96.74%. Comparing base (1415c5b) to head (5c7e9a4).

Files with missing lines	Patch %	Lines
src/lib/decuplicate.ts	97.22%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #99      +/-   ##
==========================================
+ Coverage   96.71%   96.74%   +0.03%     
==========================================
  Files          14       14              
  Lines        1064     1107      +43     
  Branches      142      150       +8     
==========================================
+ Hits         1029     1071      +42     
- Misses         34       35       +1     
  Partials        1        1              

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[codecov-commenter]

Bundle Report

Changes will increase total bundle size by 1.35kB (5.02%) ⬆️⚠️, exceeding the configured threshold of 5%.

Bundle name	Size	Change
index.js-esm	14.39kB	1.35kB (10.33%) ⬆️⚠️

Affected Assets, Files, and Routes:

view changes for bundle: index.js-esm

Assets Changed:

Asset Name	Size Change	Total Size	Change (%)
index.js	1.1kB	12.78kB	9.43% ⚠️
index.d.ts	246 bytes	1.6kB	18.1% ⚠️

Files in index.js:

• ./src/lib/extend-ranges.ts → Total Size: 1.02kB

• ./src/lib/chunkify.ts → Total Size: 2.77kB

• ./src/lib/index.ts → Total Size: 2.75kB

• ./src/lib/decuplicate.ts → Total Size: 1.41kB