feat: hierarchical scope matching for URNs

[chbgdn]

Adds support for flexible scope matching. This is required for Matrix (MSC3861) to handle dynamic URNs, like urn:matrix:device:some_id. It now correctly matches base URNs (e.g., urn:matrix:device) with their hierarchical extensions.

This logic is opt-in via the new [matrix] config section (MATRIX_SUPPORT_ENABLE).

Also improved validation by splitting the CSV scope string, which avoids accidental substring matches (e.g., api matching matrix:api).

[sebadob]

(...) which avoids accidental substring matches.

Thanks. I had that on my TODO already.

When the Matrix flow is fully working it would be very nice if you could add it to the docs about it. Just shortly mention the setup and necessary config options to set. I would create a "Guides" or "Example Configs", section or something like that. I wanted to start this since a long time already, I just did not have the time. Matrix however requires a bit more setup and this would be very helpful for others I guess.

[chbgdn]

When the Matrix flow is fully working it would be very nice if you could add it to the docs about it. Just shortly mention the setup and necessary config options to set. I would create a "Guides" or "Example Configs", section or something like that. I wanted to start this since a long time already, I just did not have the time. Matrix however requires a bit more setup and this would be very helpful for others I guess.

I actually managed to get a successful login with one more small tweak on top of this PR, so the proof of concept is working. I'll start with the guide once I've polished the remaining parts and made sure the whole flow is 100% solid.