binder: synchronize in-use stream updates

[becomeStar]

Fixes a race between newStream() and unregisterInbound() that could cause inconsistent transportInUse() notifications.

• Added listenerNotifyLock to synchronize listener callbacks and ensure mutual exclusion.
• Reconcile listenerInUse state with current numInUseStreams to avoid stale toggles under concurrent updates.
• Ensure transportInUse() is only called when the in-use state actually changes.
• Concurrency-sensitive areas have been considered; additional unit/integration tests may be added upon review.

Fixes #10917

[becomeStar]

I’m considering adding a unit test for updateInUseStreamsIfNeed() (with VisibleForTesting annotation) to verify its behavior on in-use state transitions. Would you prefer this test to be included in the same PR or in a separate one?

[kannanjgithub]

@jdcormie Ping.