feat(combos): Add require-prior-idle-ignore

[ssbb]

Some keys do not add any value to require-prior-idle-ms. The most obvious example is Space - you can't rely on Space for RPI because you can start typing with the same word (eg with combo on OU with RPI it won't trigger when you type the output but will trigger when you start typing with just output).

require-prior-idle makes the most sense for rolls that do not appear at the start of a word, such as ND. However, imagine you have a combo that outputs = at this position and want to type myvar = something. You would need to wait after pressing Space, which does not make sense. Ignoring Space here is reasonable because [space]ND is not something you typically want to type.

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.