observe

Overrides the 2-arg observe to prevent false subscriptionReady when testing pre-readiness failures.

The default BleService implementation calls observe(characteristic).onStart { onSubscription() }, which would invoke onSubscription BEFORE any pre-collection failure flow throws. This override throws BEFORE invoking onSubscription, correctly simulating "observe failed before CCCD/subscription readiness."

Pre-readiness failures are sourced (in priority order) from:

• observeBeforeSubscriptionExceptionByCharacteristic (2-arg-specific, one-shot per uuid)

• observeExceptionsByCharacteristic (shared with 1-arg observe, one-shot per uuid; defensively treated as a pre-subscription failure here so the bare onStart wrap cannot swallow it after onSubscription runs)

• observeException (global, one-shot)

For characteristics in observeNeverSubscribeCharacteristics, onSubscription is never invoked but notifications are still exposed — the returned flow is the bare SharedFlow with no onStart wrap, so emitNotification still reaches active collectors.