Report bundler-eliminated (tree-shaken) functions as uncovered

[NullVoxPopuli-ai-agent]

Fixes the remaining false positives from #22 (jagthedrummer's follow-up comments: unusedTestFunction in the store service and a top-level unusedNonClassFunction in a component both still showed as covered).

Root cause

Both functions are unexported and unreferenced, so rollup/vite tree-shakes them out of the build entirely — the bundles are byte-identical with or without them (the names only survive in .map sourcesContent). With no compiled code, V8 never sees them, the source map has no segments for their lines, and v8-to-istanbul defaults unmapped original lines to covered. Not platform-specific this time — reproduced on Linux with the exact shapes from the screenshots.

Fix

While processing each bundle, the report now records which original-source lines have at least one source-map segment. After merging, each reported original file is parsed with acorn and function-like declaration spans are collected (function/class declarations, function/arrow variable initializers). A span with no mapped lines in any bundle was eliminated by the bundler: its statement counts are zeroed and an uncovered function entry is added. A span with even one mapped line is left alone — the bundle kept it, so real V8 data (or the synthetic-method pass) already decides its coverage.

To parse original .gjs/.gts files, <template>…</template> spans are blanked to an offset-preserving 0 placeholder and decorators (@tracked, @action('x'), …) are blanked to spaces — parse-validity is all that matters. Files that still fail to parse are skipped rather than guessed at.

Scenario changes

vite-app-using-v2-addon-js now contains both shapes from the issue report, replicated from the screenshots:

• app/services/store.js — unusedTestFunction() (unexported, never called)
• app/components/counter.gjs — unusedNonClassFunction() (top-level, outside the class)

Before this fix both reported 100% covered; now store.js reports 0/1 functions with its lines uncovered, and counter.gjs reports the function uncovered alongside the two never-called class methods. Regression assertions added for both, plus the store.js entry itself.

All 22 tests across the three scenarios pass, lint clean.

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