fix(paths): add path verification

[dkundel]

Adds checks for:

• shorter than 256 characters
• none of the following characters ;,?:@+&$()' "
• starts with a /

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[philnash]

Code looks good to me. And yay for the first of the tests!

Are the only invalid characters [;,?:@+&$()' ? Could you, for example, use an emoji in a path?

[dkundel]

I merged this for now to ship it but I created a follow up issue for the emoji situation. It might just mean that when we create the paths from filenames we have to convert those into escaped characters using the URL class