Fix issue stripping multi-character delimiters

[rolandwalker]

Description

• strip by the whole delimiter, not the character/s
• strip only from the end
• add tests for delimitercommand.py

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]

Codex Review

No correctness or security issues found in the PR changeset (9432311).

The core fix in mycli/packages/special/delimitercommand.py is correct: replacing strip(delimiter) with suffix slicing prevents accidental removal of delimiter characters from the start of statements when delimiters are multi-character.

Test coverage is improved with targeted regression tests in test/pytests/test_delimitercommand.py, including the multi-character delimiter case and delimiter-switch flow.

Residual risk: I couldn’t execute tests in this environment because uv is unavailable (uv: command not found), so this is a static review only.

[j-bennet]

Nice!