Allow --with-requirements to load extensionless inline-metadata scripts (#16744)

Resolves https://github.com/astral-sh/uv/issues/16732

This diff treats extensionless files that contain
[PEP 723](https://peps.python.org/pep-0723/) metadata as scripts when
resolving `--with-requirements`, so inline metadata works even when the
script doesn’t end in `.py`.

---------

Co-authored-by: Charlie Marsh <charlie.r.marsh@gmail.com>

crates/uv-scripts/src/lib.rs

@@ -175,28 +175,16 @@ impl Pep723Script {
     ///
     /// See: <https://peps.python.org/pep-0723/>
     pub async fn read(file: impl AsRef<Path>) -> Result<Option<Self>, Pep723Error> {
-        let contents = fs_err::tokio::read(&file).await?;
+        let file = file.as_ref();
+        let contents = fs_err::tokio::read(file).await?;
+        Self::from_contents(file, &contents)
+    }
 
-        // Extract the `script` tag.
-        let ScriptTag {
-            prelude,
-            metadata,
-            postlude,
-        } = match ScriptTag::parse(&contents) {
-            Ok(Some(tag)) => tag,
-            Ok(None) => return Ok(None),
-            Err(err) => return Err(err),
-        };
-
-        // Parse the metadata.
-        let metadata = Pep723Metadata::from_str(&metadata)?;
-
-        Ok(Some(Self {
-            path: std::path::absolute(file)?,
-            metadata,
-            prelude,
-            postlude,
-        }))
+    /// Read the PEP 723 `script` metadata from a Python file using blocking I/O.
+    pub fn read_sync(file: impl AsRef<Path>) -> Result<Option<Self>, Pep723Error> {
+        let file = file.as_ref();
+        let contents = fs_err::read(file)?;
+        Self::from_contents(file, &contents)
     }
 
     /// Reads a Python script and generates a default PEP 723 metadata table.
@@ -349,6 +337,29 @@ impl Pep723Script {
             .and_then(|uv| uv.sources.as_ref())
             .unwrap_or(&EMPTY)
     }
+
+    fn from_contents(path: &Path, contents: &[u8]) -> Result<Option<Self>, Pep723Error> {
+        let script_tag = match ScriptTag::parse(contents) {
+            Ok(Some(tag)) => tag,
+            Ok(None) => return Ok(None),
+            Err(err) => return Err(err),
+        };
+
+        let ScriptTag {
+            prelude,
+            metadata,
+            postlude,
+        } = script_tag;
+
+        let metadata = Pep723Metadata::from_str(&metadata)?;
+
+        Ok(Some(Self {
+            path: std::path::absolute(path)?,
+            metadata,
+            prelude,
+            postlude,
+        }))
+    }
 }
 
 /// PEP 723 metadata as parsed from a `script` comment block.