uv-resolver: error during installation for conflicting extras
This collects ALL activated extras while traversing the lock file to
produce a `Resolution` for installation. If any two extras are activated
that are conflicting, then an error is produced.
We add a couple of tests to demonstrate the behavior. One case is
desirable (where we conditionally depend on `package[extra]`) and the
other case is undesirable (where we create an uninstallable lock file).
Fixes #9942, Fixes #10590
