Since rack 3 is now supported by Rails, it seems important to ensure that this middleware has a proper support for it. Issues with rack 3 are difficult to notice or debug. To help prevent issues with compatibility and the time that it takes to manually debug and resolve those - I suggest that we integrate `Rack::Lint` into the test suite.

Rack::Lint would ensure that middleware adheres to the SPEC.

Please be patient, since I' still figuring out how this works ;-)

Related documentation (for me to read through multiple times):
- https://github.com/rack/rack/blob/744f92d099653f873ced3380e425a6f82f0c6c6c/UPGRADE-GUIDE.md?plain=1#L185
- https://github.com/rack/rack/blob/744f92d099653f873ced3380e425a6f82f0c6c6c/SPEC.rdoc

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Co-authored-by: Julik Tarkhanov <me@julik.nl>

Make sure fingerprinting works with non-rewindable request bodies, and add tests to make sure everything contributes to the fingerprint correctly

Something that supports to_ary "just" supports it anyway

as there are quite a few

as it doesn't make much sense with Rack 3.0 streaming bodies - we may be able to read out the request body, or we may not be able to. If we are not able - the fingerprint will be the same.

as Lint is appropriately hinting

because if it works on 2.7 it will work on 3 just as well, and we are not using 3.x specific syntax (and have standardrb rules configured accordingly)