refactor(bundle-size): drop dead code paths

[layershifter]

Summary

Mechanical hygiene with no behavioural change:

• Audit Utils.ts to remove dead helpers and inline tiny one-shot utilities at call sites. getRadioButtonGroup keeps its prior find-last-checked semantics (single-pass loop, no Array.from/.filter/.find chain); disposeInstanceContext keeps its eager elementByUId / containerBoundingRectCache clears before unhooking.
• Switch MutationEvent removed/added node loops from index-based for to for…of (slightly shorter emit, easier to read).
• Drop dead moz / ms branches from the Outline fullscreen-event detection cascade. Firefox unprefixed fullscreenchange since v64 (Dec 2018) and the ms* variant was IE 11 / legacy EdgeHTML — both excluded by .browserslistrc. The Safari webkit branch stays: Safari 15–16.3 still needs it (unprefixed since 16.4).

[github-actions]

📊 Bundle size report

Package & Exports	Baseline (minified/GZIP)	PR	Change
tabster all exports	111.844 kB 30.077 kB	111.331 kB 29.989 kB	-513 B -88 B
tabster createTabster (core)	38.553 kB 11.447 kB	38.354 kB 11.39 kB	-199 B -57 B
tabster focusable.findAll	38.576 kB 11.456 kB	38.377 kB 11.399 kB	-199 B -57 B
tabster focusable.findLast	38.577 kB 11.455 kB	38.378 kB 11.398 kB	-199 B -57 B
tabster focusable.findNext	38.577 kB 11.455 kB	38.378 kB 11.398 kB	-199 B -57 B
tabster focusable.findPrev	38.577 kB 11.455 kB	38.378 kB 11.398 kB	-199 B -57 B
tabster getCrossOrigin	108.658 kB 29.354 kB	108.145 kB 29.263 kB	-513 B -91 B
tabster getDeloser	47.984 kB 13.733 kB	47.785 kB 13.677 kB	-199 B -56 B
tabster getGroupper	45.779 kB 13.118 kB	45.58 kB 13.066 kB	-199 B -52 B
tabster getModalizer	47.622 kB 13.87 kB	47.423 kB 13.82 kB	-199 B -50 B
tabster getMover	53.229 kB 15.367 kB	53.03 kB 15.32 kB	-199 B -47 B
tabster getObservedElement	44.337 kB 13.01 kB	44.138 kB 12.967 kB	-199 B -43 B
tabster getOutline	47.522 kB 13.714 kB	47.054 kB 13.636 kB	-468 B -78 B
tabster getRestorer	41.272 kB 12.058 kB	41.073 kB 12.002 kB	-199 B -56 B

_{🤖 This report was generated against 43ddff99f4472476797bfb988b70eba20ff7da0d}