Improve query cancellation on control-c

[rolandwalker]

Description

• sqlexecute.run() no longer returns a tuple, but a Generator of SQLResults
• move sqlexecute.connect() within a try block
• clarify inner error as e2
• grammar and spelling in commentary
• if raising a CommandNotFound(), show the command (this can be part of the relevant backtrace)

Due to the first and second bullet, an interrupted query would indeed be cancelled, but the user would at minimum receive poor feedback, and the mycli session could also end.

It might also be desirable to tell click not to handle KeyboardInterrupt.

Checklist

• I added this contribution to the changelog.md file.
• I added my name to the AUTHORS file (or it's already there).
• To lint and format the code, I ran

  uv run ruff check && uv run ruff format && uv run mypy --install-types .

[github-actions]

No correctness or security regressions stood out in the PR diff itself.

Findings:

1. Missing test coverage for the new Ctrl-C cancellation flow in mycli/main.py:1212.
   Add an integration test that simulates KeyboardInterrupt during query execution and asserts:

• sqlexecute.connect() is attempted inside the handler,
• kill <connection_id> is issued,
• user-facing feedback is emitted for both success and failure paths,
• the session remains usable after interruption.

2. Missing test coverage for the new command text in CommandNotFound at mycli/packages/special/main.py:136.
   Add a unit test for special.execute() with an unknown command to verify the exception message includes the command name and doesn’t alter normal SQL fallback behavior through SQLExecute.run().

Residual risk:

• The PR changes error/interrupt handling behavior but adds no tests, so regressions are most likely in interrupt edge paths rather than normal execution.