Feature request: add cancellation support for TransferSIPParticipant API

[shwetd19]

CC : @mike-r-mclaughlin

Description

Currently, there's no mechanism to cancel an ongoing TransferSIPParticipant() operation after it has been initiated. This leads to race conditions and conflicting states when users change their mind mid-transfer or when the system needs to handle interruptions.

Current Behavior

When TransferSIPParticipant() is called:

• The transfer process begins immediately
• There's no way to stop or cancel the transfer
• Any subsequent operations (like starting a new workflow) can run concurrently with the transfer
• This can lead to undefined behavior and poor user experience

Example Scenario

User: "I need billing"
System: Initiates TransferSIPParticipant() to billing department
User: "Wait, actually I want to schedule an appointment"
System: Starts appointment scheduling workflow
[Problem: Transfer continues in background while appointment scheduling begins]

Proposed Solution

Add a cancellation mechanism for TransferSIPParticipant() that could work in one of these ways:

1. Cancel Method:

transfer = await room.TransferSIPParticipant(...)
await transfer.cancel()  # New method

2. Context Manager Approach:

with await room.TransferSIPParticipant(...) as transfer:
    try:
        # Transfer in progress
    except UserInterruption:
        await transfer.cancel()

3. Cancellation Token:

cancellation_token = CancellationToken()
await room.TransferSIPParticipant(..., cancellation_token=cancellation_token)
# Later when needed:
cancellation_token.cancel()

Technical Considerations

Implementation Requirements

1. Thread-safe cancellation mechanism
2. Proper cleanup of resources
3. Clear state management during cancellation
4. Event notifications for cancellation status

Edge Cases to Handle

• Cancellation during different stages of transfer
• Multiple rapid cancel requests
• Partial transfer states
• Resource cleanup
• Connection handling

This request comes from production usage where voice assistants need to handle dynamic user interactions and change of intent during transfers.