fix: do not cancel CodeMirror compose beforeChange

[Steve0x2a]

Controlled beforeChange currently calls data.cancel() for every origin, including CodeMirror 5 IME/dead-key changes (origin === "*compose"). Cancelling those prevents composition from committing (' + e → é, macOS double-space → period). The UnControlled wrapper does not cancel.

This skips data.cancel() when data.origin === "*compose", still notifies onBeforeChange, and avoids replaying the change with setValue/replaceRange while the native compose change is in flight. Undo/redo and the emulating path are unchanged.

Credits @mblagojevic10 for the report and the *compose diagnosis.

Fixes #327

Test plan

• New unit: Controlled beforeChange with origin: "*compose" is not cancelled, and the composed character is applied
• New unit: updating value from onBeforeChange during compose does not duplicate the character
• Existing suite (npm test): 46 passed