[pika] Fix connection parameter for callbacks

[srittau]

The callbacks provided to a connection get passed the connection as first argument. While this was correctly typed as Self in the base Connection class, the concrete Connection class was used in sub-classes. Fixed to use Self in sub-classes as well.

[github-actions]

Diff from mypy_primer, showing the effect of this PR on open source code:

zulip (https://github.com/zulip/zulip)
- zerver/lib/queue.py:286: error: Argument "on_open_error_callback" to "ExceptionFreeTornadoConnection" has incompatible type "Callable[[Connection, str | Exception], None]"; expected "Callable[[Connection, BaseException], object] | None"  [arg-type]
+ zerver/lib/queue.py:286: error: Argument "on_open_error_callback" to "ExceptionFreeTornadoConnection" has incompatible type "Callable[[Connection, str | Exception], None]"; expected "Callable[[ExceptionFreeTornadoConnection, BaseException], object] | None"  [arg-type]
- zerver/lib/queue.py:287: error: Argument "on_close_callback" to "ExceptionFreeTornadoConnection" has incompatible type "Callable[[Connection, Exception], None]"; expected "Callable[[Connection, BaseException], object] | None"  [arg-type]
+ zerver/lib/queue.py:287: error: Argument "on_close_callback" to "ExceptionFreeTornadoConnection" has incompatible type "Callable[[Connection, Exception], None]"; expected "Callable[[ExceptionFreeTornadoConnection, BaseException], object] | None"  [arg-type]