Rename uv-traits and split into separate modules (#2674)

This is driving me a little crazy and is becoming a larger problem in
#2596 where I need to move more types (like `Upgrade` and `Reinstall`)
into this crate. Anything that's shared across our core resolver,
install, and build crates needs to be defined in this crate to avoid
cyclic dependencies. We've outgrown it being a single file with some
shared traits.

There are no behavioral changes here.

crates/uv-resolver/tests/resolver.rs

@@ -20,7 +20,7 @@ use uv_resolver::{
     DisplayResolutionGraph, InMemoryIndex, Manifest, Options, OptionsBuilder, PreReleaseMode,
     Preference, ResolutionGraph, ResolutionMode, Resolver,
 };
-use uv_traits::{
+use uv_types::{
     BuildContext, BuildIsolation, BuildKind, NoBinary, NoBuild, SetupPyStrategy, SourceBuildTrait,
 };