Fix ThreadedVNCClientProxy to use bound methods

[sibson]

Summary

• Fix TypeError: VNCDoToolClient.captureScreen() missing 1 required positional argument: 'fp' #297: ThreadedVNCClientProxy.__getattr__ was using unbound methods from the VNCDoToolClient class and relying on the Twisted deferred chain to pass the protocol instance as self. This caused TypeError: VNCDoToolClient.captureScreen() missing 1 required positional argument: 'fp' when the chain result diverged from the protocol.
• Relates to API documentation: self via Deferred #266: Any exception permanently switched the deferred to errback mode, making all subsequent proxy calls fatal. The fix adds a restore_protocol callback via addBoth that always returns the deferred chain to callback mode.
• Adds unit tests for ThreadedVNCClientProxy (previously untested).

Changes

1. Use bound methods from self.protocol (the instance) instead of unbound methods from the class
2. Don't pass protocol as first arg to maybeDeferred — bound methods already have self
3. Add restore_protocol callback to ensure the deferred chain always recovers after each call

Test plan

• All 8 new unit tests pass, all existing tests pass
• Functional test with Xvnc (requires Xvnc)
• New tests cover:
  • Basic method proxying with bound methods
  • Args/kwargs passed correctly
  • Methods returning Deferreds (like captureScreen)
  • Multiple sequential calls
  • Chain recovery after a failed Deferred
  • Chain recovery after a raised exception
  • Non-callable attribute access
  • Missing attribute raises AttributeError

🤖 Generated with Claude Code

[pmhahn]

I just a s short look and it looks okay.
I no longer have my test environment with Xvnc myself handy, so couldn't test it also. Maybe I still have it on a different computer.