fix(Android): ignore reload callbacks after teardown

[OskarEichler]

Problem and fix

Both Android reload handlers replaced their listener with null during teardown. A late dev-bundle onSuccess() callback then dereferenced that null listener:

• JsDevReloadHandler can receive a bundle-download completion after its NavigationActivity has been destroyed and removed
• ReloadHandler remained callable after destroy() through the same callback interface

This change restores the no-op listener each handler already uses before initial registration. Late callbacks are safely ignored without retaining the destroyed listener or adding nullable checks to every call site.

Regression coverage

• JsDevReloadHandlerTest removes an activity listener and invokes a late success callback
• ReloadListenerTest destroys the generic handler and invokes a late success callback

Both exact baseline paths throw NullPointerException; the fixed focused suite passes 3/3.

Verification

• focused reload suites: 3/3 passed
• full Android unit suite: 699 passed, 2 skipped, 0 failed
• Android debug Java/Kotlin compilation passed
• git diff --check passed

Breaking changes

None. Callbacks after teardown are now ignored instead of crashing.