fix: add callback_interruption to Conversation/AsyncConversation

[SomSamantray]

Issue

Conversation / AsyncConversation expose a callback for every WebSocket event type the wrapper dispatches — agent_response, user_transcript, audio_alignment, etc. — except interruption. When an interruption event arrived, the wrapper only called audio_interface.interrupt() internally; there was no way for a caller to observe the event, and text-only (no audio_interface) integrations couldn't observe it at all.

Closes #672.

Fix

Added an optional callback_interruption parameter to both Conversation and AsyncConversation, following the same pattern already used for the other callbacks. It fires with a new InterruptionEvent(event_id, reason) dataclass (mirroring the existing AudioEventAlignment pattern) in addition to the existing audio_interface.interrupt() call, in both the sync and async paths.

Added test coverage for both paths.

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Note

Low Risk
Backward-compatible optional callback and additive dataclass; existing callers unchanged when the callback is omitted.

Overview
Adds optional callback_interruption on sync Conversation and AsyncConversation so apps can observe WebSocket interruption events, including text-only sessions without an audio interface.

Introduces InterruptionEvent (event_id, optional reason) and wires interruption handling to still call audio_interface.interrupt() when present, then invoke the callback if set. Sync and async message paths share the same behavior.

Adds unit tests for callback invocation with/without audio, default None callback, and missing reason on the wire event.

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