Accept quoted file paths in the IPython dotenv magic

[FanWu-ai]

Summary

IPython's POSIX argument parser preserves the quote characters used to group a filename. As a result, %dotenv "my project/app.env" reports cannot find .env file even when the file exists.

On non-Windows platforms, remove a matching pair of outer single or double quotes before looking up the file. This also lets quoted absolute and ~/ paths reach the existing path-resolution behavior. Backslashes and internal apostrophes are preserved. Windows keeps its existing native argument parsing, including literal apostrophes in filenames.

Tests

• Integration cases load real relative, absolute, and home-directory paths containing spaces, with both POSIX quote styles and -o. Native Windows still exercises double quotes; unsupported single-quote grouping is expected to raise UsageError without changing the environment.
• Additional cases cover Windows-style backslashes, internal apostrophes, and an actual filename with literal outer apostrophes. Three simulated Windows post-parser cases verify filenames are preserved unchanged.
• Ten added regression cases fail against the original source; five added compatibility controls pass before and after the change.
• Full clean baseline: 288 passed. Final full suite: 303 passed, zero skipped, on Linux/Python 3.12.14. Native Windows execution is left to hosted CI and is not claimed passed.
• Tox lint (Ruff lint/format and mypy Python targets 3.10 through 3.14), manifest, coverage report, pinned pre-commit hooks, strict MkDocs build, isolated sdist/wheel build, and git diff --check all passed.

AI assistance: prepared and tested with OpenAI Codex, including independent automated review. No human review or hosted CI pass is claimed.