Strip trailing newlines with \e <filename>

[rolandwalker]

Description

Trailing newlines were stripped in other variations of \e, but not when reading from a file. Stripping helps place the cursor in the expected place when returning to the prompt.

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]

Review summary
No correctness or security regressions found in the code change itself. One test gap.

Findings

1. Missing test coverage for the \e <filename> branch that now strips trailing newlines. This is the only behavior change in the PR and isn’t exercised by existing tests. Add a test in test/test_special_iocommands.py that writes a temp file with a trailing newline (and ideally multiple) and asserts open_external_editor(filename=...) returns the content without trailing \n. This should be gated to non-Windows like the other editor test, or account for \r\n.
   File: mycli/packages/special/iocommands.py:188

If you want, I can draft the test.