perf: honor cacheAsBitmap + skip no-op timeline mtx writes

[roncarbot]

Summary

• Add HONOR_CACHE_AS_BITMAP (default true): SWF-safe path so AS3 cacheAsBitmap sticks without requiring USE_UNSAFE_CACHE_AS_BITMAP. Legacy unsafe flag still OR-enables.
• Timeline update_mtx_all / scale_rot / pos / colorTransform skip identical hold-frame rewrites that previously dirtied parent caches every tick.
• E9: Add HONOR_NATIVE_BLENDS (default true): Flash-native blendMode values (LAYER/ERASE/…) return through the getter so Diggy GroundFG LAYER + ERASE child engages ContainerNode.renderToImage / sticky CacheRenderer. Non-native blends still need USE_UNSAFE_BLENDS. Kill-switch: HONOR_NATIVE_BLENDS=false.

Pairs with awayjs/renderer#35 and awayjs/view#7 (E8 sticky CacheRenderer).

Test plan

• Diggy title: cacheAsBitmap setter roundtrips (honored: 20/20)
• Diggy GroundMap/HoleCircle AS writes honor when gameplay unlocked
• Kill-switch: Settings.HONOR_CACHE_AS_BITMAP=false restores legacy no-op
• Diggy GroundFG: after CreateMap, blendMode==="layer", ERASE child, renderToImage=true, CacheRenderer sticky (contentDirty=false)
• Diggy gameplay: 50 → 33.4 ms, draws ~254 → ~207; dig-hole visual OK
• Diggy title E8 kids smoke unchanged: 16.7 ms / ~11 draws / cacheRenders=0
• Kill-switch: Settings.HONOR_NATIVE_BLENDS=false restores blend getter empty-string gate

Diggy gameplay unlock (2026-09-09)

Coolmath host: http://localhost.coolmathgames.com:8080/Diggy_fixed.html. HoleCircle remains BitmapData stamp (off-list). E9 LAYER path is the in-level CacheRenderer engagement.

E10 Diggy menu (authoring / harness — no new scene commit)

• MainMenu parallax l1–l7 content-static; mouse parallax is transform-only → E8 sticky CacheRenderer.
• Per-layer cacheAsBitmap: 100 → 16.7 ms, draws 370 → ~53 GL / ~105 away, cacheRenders=0, 30/30 fps.
• whole-menu cache discarded (cacheRenders=1 thrash from UI templates).
• Gameplay leftover: GroundBack ~1223 fills but kids churn → whole-cache thrash (discarded). Dig-dirty: m_mask.graphics → GroundFG LAYER RTT ~10–20 ms/rebuild (expected).