Ignore tags in universal resolution (#4174)

## Summary

If a package lacks a source distribution, and we can't find a compatible
wheel for the current platform, we need to just _assume_ that the
package will have a valid wheel on all platforms on which it's
requested; if not, we raise an error at install time.

It's possible that we can be smarter about this over time. For example,
if the package was requested _only_ for macOS, we could verify that
there's at least one macOS-compatible wheel. See the linked issue for
more details.

Closes https://github.com/astral-sh/uv/issues/4139.

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

@@ -131,7 +131,7 @@ impl<'a, Context: BuildContext, InstalledPackages: InstalledPackagesProvider>
         options: Options,
         python_requirement: &'a PythonRequirement,
         markers: Option<&'a MarkerEnvironment>,
-        tags: &'a Tags,
+        tags: Option<&'a Tags>,
         flat_index: &'a FlatIndex,
         index: &'a InMemoryIndex,
         hasher: &'a HashStrategy,