Fix/android detach cancels render

[istarkov]

The bug

On Android a formula can end up permanently invisible: it occupies exactly the right
space (measurement is synchronous and fine), draws nothing, and only a full remount
brings it back. onError fires with the confusing StandaloneCoroutine was cancelled.

Reproduction

Got this on real App, and it's reproducible ;-)

demo/react-native-expo (upgraded to Expo SDK 57 / RN 0.86) has a new Detach-cancel
case that reproduces this deterministically: 32 formulas mount inside opacity: 0
wrappers that are revealed one frame later. Dropping the style makes the wrappers
eligible for Fabric view flattening, so the commit re-parents them
(SurfaceMountingManager.removeViewAt + addView) — transiently detaching every formula
while its render job is still in flight. Kill + relaunch the app (cold start is the most
reliable: the first job blocks on the KaTeX font load, keeping all 32 pending):

Broken (this branch's parent)	Fixed (this branch)
red dot, rendered 0/32 · errors 32, blank boxes	green dot, rendered 32/32 · errors 0

Root cause

1. onDetachedFromWindow cancels the pending renderJob — but the detach is only
   transient (the flattening re-parent above; also view moves, RecyclerView, RN
   #38567). The view comes right
   back; its job doesn't.
2. Nothing restarts it: every rerender() trigger is a prop setter guarded by
   if (field == value) return, and the props never change again → blank forever.
3. catch (e: Throwable) swallows the CancellationException and reports it as a render
   error. For a CancellationException to terminate a coroutine properly it must reach
   the top of the call stack uncaught.

The fix

Applied to RaTeXView.kt + RaTeXInlineView.kt (react-native) and the standalone
platforms/android RaTeXView.kt — the same pattern Coil uses in
ViewTargetRequestManager
(cancel on detach is only safe when paired with restart on attach):

• onAttachedToWindow re-kicks the render when nothing is rendered, content is
  non-blank, and no job is in flight (a normal attach is a no-op).
• Rethrow CancellationException instead of turning it into an error state + bogus
  onError (see kotlinx.coroutines#1814).
• Standalone copy only: cancel just the job on detach, not the whole scope (+
  SupervisorJob) — a cancelled scope ignores every future launch, killing the view
  for good.

Validation

• Demo case above: 0/32 → 32/32 on cold start.
• Consumer app (RN 0.86 + expo-router, Pixel emulator): cold deep-link into a 13-formula
  document went from mostly-blank to all rendered, pixel-identical across a remount
  cycle (pr-screenshots/android-broken-blank-formulas.png /
  android-fixed-all-formulas.png).
• iOS unaffected (no detach-cancel lifecycle in its render path).

Consumer-side tip (independent of this fix): pinning the revealing wrapper with
collapsable={false} keeps its flattening status stable and avoids the detach wave
entirely.

[erweixin]

Thank you for putting this PR together — this is an excellent, very carefully documented fix.

Really thoughtful contribution. Thanks again for digging into this and for the thorough validation notes.