fix(behaviors): Deactivate caps_word after modified numerics

[matthewtodd]

Fixes #2723.

The caps_word behavior now strictly honors [A-Za-z0-9_] as the default continuation characters. (Previously !@#$%^&*() were mistakenly also honored.)

I discovered this by trying to use caps_word for comment markers like FIXME(mt): and finding that the opening left parenthesis didn't deactivate caps_word.

PR check-list

• Branch has a clean commit history
• Additional tests are included, if changing behaviors/core code that is testable.
• Proper Copyright + License headers added to applicable files (Generally, we stick to "The ZMK Contributors" for copyrights to help avoid churn when files get edited)
• Pre-commit used to check formatting of files, commit messages, etc.
• Includes any necessary documentation changes.