Show package list with `pip freeze --quiet` (#16491)

## Summary

Closes https://github.com/astral-sh/uv/issues/16178.

crates/uv/src/commands/pip/freeze.rs

@@ -83,7 +83,7 @@ pub(crate) fn pip_freeze(
             }
         })
         .dedup()
-        .try_for_each(|dist| writeln!(printer.stdout(), "{dist}"))?;
+        .try_for_each(|dist| writeln!(printer.stdout_important(), "{dist}"))?;
 
     // Validate that the environment is consistent.
     if strict {

crates/uv/src/commands/pip/list.rs

@@ -1,7 +1,6 @@
 use std::cmp::max;
 use std::fmt::Write;
 
-use anstream::println;
 use anyhow::Result;
 use futures::StreamExt;
 use itertools::Itertools;
@@ -181,7 +180,7 @@ pub(crate) async fn pip_list(
                 })
                 .collect_vec();
             let output = serde_json::to_string(&rows)?;
-            println!("{output}");
+            writeln!(printer.stdout_important(), "{output}")?;
         }
         ListFormat::Columns if results.is_empty() => {}
         ListFormat::Columns => {
@@ -255,13 +254,18 @@ pub(crate) async fn pip_list(
             }
 
             for elems in MultiZip(columns.iter().map(Column::fmt).collect_vec()) {
-                println!("{}", elems.join(" ").trim_end());
+                writeln!(printer.stdout_important(), "{}", elems.join(" ").trim_end())?;
             }
         }
         ListFormat::Freeze if results.is_empty() => {}
         ListFormat::Freeze => {
             for dist in &results {
-                println!("{}=={}", dist.name().bold(), dist.version());
+                writeln!(
+                    printer.stdout_important(),
+                    "{}=={}",
+                    dist.name().bold(),
+                    dist.version()
+                )?;
             }
         }
     }

crates/uv/tests/it/pip_freeze.rs

@@ -453,3 +453,32 @@ fn freeze_nonexistent_path() {
     ----- stderr -----
     ");
 }
+
+#[test]
+fn freeze_with_quiet_flag() -> Result<()> {
+    let context = TestContext::new("3.12");
+
+    let requirements_txt = context.temp_dir.child("requirements.txt");
+    requirements_txt.write_str("MarkupSafe==2.1.3\ntomli==2.0.1")?;
+
+    // Run `pip sync`.
+    context
+        .pip_sync()
+        .arg(requirements_txt.path())
+        .assert()
+        .success();
+
+    // Run `pip freeze` with `--quiet` flag.
+    uv_snapshot!(context.pip_freeze().arg("--quiet"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    markupsafe==2.1.3
+    tomli==2.0.1
+
+    ----- stderr -----
+    "###
+    );
+
+    Ok(())
+}