Implement --show-version-specifiers for tree (#5240)

## Summary
resolves https://github.com/astral-sh/uv/issues/5217

## Test Plan
existing tests pass (should be perfectly backwards compatible) + added a
few tests to cover the new functionality. in particular, in addition to
the simple use of `--show-version-specifiers`, its interaction with
`--invert` and `--package` flags are tested.

crates/uv-cli/src/lib.rs

@@ -2764,4 +2764,8 @@ pub struct DisplayTreeArgs {
     /// Show the reverse dependencies for the given package. This flag will invert the tree and display the packages that depend on the given package.
     #[arg(long, alias = "reverse")]
     pub invert: bool,
+
+    /// Show the version constraint(s) imposed on each package.
+    #[arg(long)]
+    pub show_version_specifiers: bool,
 }