Trim trailing whitespace and normalize newlines.

[bdice]

Description

Closes #1632.

This PR uses hooks provided by https://github.com/pre-commit/pre-commit-hooks to enforce that trailing whitespace is trimmed and that all files have consistent line endings.

I also updated the devcontainer configuration to trim trailing whitespace and end files with \n by default.

Checklist

• New or existing tests cover these changes.
• The documentation is up to date with these changes.