feat: support NO_COLOR and FORCE_COLOR env vars (#3979)

## Summary

Closes #3955

Adds explicit support to `NO_COLOR` and `FORCE_COLOR` via
GlobalSettings.

The order, per specs is now `NO_COLOR` > `FORCE_COLOR` > `color`.

This PR is a backup plan pending rust-cli/anstyle#192.

## Test Plan

Tested all cases locally for now; I didn't see existing tests for
GlobalSettings parsing.

README.md

@@ -592,6 +592,8 @@ In addition, uv respects the following environment variables:
 - `MACOSX_DEPLOYMENT_TARGET`: Used with `--python-platform macos` and related variants to set the
   deployment target (i.e., the minimum supported macOS version). Defaults to `12.0`, the
   least-recent non-EOL macOS version at time of writing.
+- `NO_COLOR`: Disable colors. Takes precedence over `FORCE_COLOR`. See [no-color.org](https://no-color.org).
+- `FORCE_COLOR`: Enforce colors regardless of TTY support. See [force-color.org](https://force-color.org).
 
 ## Versioning
 

crates/uv/src/settings.rs

@@ -46,8 +46,20 @@ impl GlobalSettings {
         Self {
             quiet: args.quiet,
             verbose: args.verbose,
-            color: if args.no_color {
+            color: if args.no_color
+                || std::env::var_os("NO_COLOR")
+                    .filter(|v| !v.is_empty())
+                    .is_some()
+            {
                 ColorChoice::Never
+            } else if std::env::var_os("FORCE_COLOR")
+                .filter(|v| !v.is_empty())
+                .is_some()
+                || std::env::var_os("CLICOLOR_FORCE")
+                    .filter(|v| !v.is_empty())
+                    .is_some()
+            {
+                ColorChoice::Always
             } else {
                 args.color
             },