uv: use ResolverEnvironment instead of ResolverMarkers

This updates the surrounding code to use the new ResolverEnvironment
type. In some cases, this simplifies caller code by removing case
analysis. There *shouldn't* be any behavior changes here. Some test
snapshots were updated to account for some minor tweaks to error
messages.

I didn't split this up into separate commits because it would have been
too difficult/costly.

crates/uv-resolver/src/lib.rs

@@ -19,8 +19,8 @@ pub use resolution::{
 pub use resolution_mode::ResolutionMode;
 pub use resolver::{
     BuildId, DefaultResolverProvider, InMemoryIndex, MetadataResponse, PackageVersionsResult,
-    Reporter as ResolverReporter, Resolver, ResolverMarkers, ResolverProvider, VersionsResponse,
-    WheelMetadataResult,
+    Reporter as ResolverReporter, Resolver, ResolverEnvironment, ResolverProvider,
+    VersionsResponse, WheelMetadataResult,
 };
 pub use version_map::VersionMap;
 pub use yanks::AllowedYanks;