Make tags non-required for fetching wheel metadata (#2700)

## Summary

This looks like a big change but it really isn't. Rather, I just split
`get_or_build_wheel` into separate `get_wheel` and `build_wheel` methods
internally, which made `get_or_build_wheel_metadata` capable of _not_
relying on `Tags`, which in turn makes it easier for us to use the
`DistributionDatabase` in various places without having it coupled to an
interpreter or environment (something we already did for
`SourceDistributionBuilder`).

crates/uv-resolver/src/resolver/mod.rs

@@ -129,7 +129,7 @@ impl<'a, Context: BuildContext + Send + Sync> Resolver<'a, DefaultResolverProvid
     ) -> Result<Self, ResolveError> {
         let provider = DefaultResolverProvider::new(
             client,
-            DistributionDatabase::new(build_context.cache(), tags, client, build_context),
+            DistributionDatabase::new(build_context.cache(), client, build_context),
             flat_index,
             tags,
             PythonRequirement::new(interpreter, markers),