Check Requires-Python before other dependencies

[uranusjr]

This makes the resolver fail quicker when there's a interpreter version conflict, and avoid additional (useless) downloads.

Fix #9925.

[webknjaz]

This is nice. Do you want to add a test ensuring that no other checks happen once there's a Python version mismatch?

[uranusjr]

Test added. I also changed the implementation to use Provider.get_preference() instead, which is less magical to me than relying on the dependencies’ internal ordering.