Support build constraints (#5639)

## Summary

Partially resolves #5561. Haven't added overrides support yet but I can
add it tomorrow if the current approach for constraints is ok.

## Test Plan

`cargo test`

Manually checked trace logs after changing the constraints.

crates/uv-resolver/src/manifest.rs

@@ -86,6 +86,12 @@ impl Manifest {
         }
     }
 
+    #[must_use]
+    pub fn with_constraints(mut self, constraints: Constraints) -> Self {
+        self.constraints = constraints;
+        self
+    }
+
     /// Return an iterator over all requirements, constraints, and overrides, in priority order,
     /// such that requirements come first, followed by constraints, followed by overrides.
     ///