fix(renderer): stroke dashed lines separately

[Komzpa]

Summary

• avoid batching dashed line and casing features into one accumulated canvas path
• keep solid line batching intact for the existing performance path
• add a regression test that proves dashed features get independent strokes while solid features still share a stroke

Fixes #61.

Validation

• npm test

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Batch lines when dash pattern normalizes to solid

render now blocks batching whenever style.dashes is truthy, but Kothic.path treats many truthy dash values (for example [0, 0], [0, 2], or non-numeric entries) as solid by normalizing them to [] in src/renderer/path.js. In those cases, this change forces one stroke per feature even though the rendered line is solid, which regresses the “solid lines still share a stroke” behavior and can reintroduce per-feature seams/perf overhead on split geometries.

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