Update pubgrub to use a dependency provider (#2648)

With https://github.com/pubgrub-rs/pubgrub/pull/190, pubgrub attaches
all types to a dependency provider to reduce the number of generics. We
need a dummy dependency provider now to emulate this. On the plus side,
pep440_rs drops its pubgrub dependency.

crates/uv-resolver/src/lib.rs

@@ -20,6 +20,7 @@ mod bare;
 mod candidate_selector;
 mod constraints;
 mod dependency_mode;
+mod dependency_provider;
 mod editables;
 mod error;
 mod finder;