Allow selection of debug build interpreters (#11520)

Extends the `PythonVariant` logic to support interpreters with the debug
flag enabled.

crates/uv-python/fetch-download-metadata.py

@@ -142,6 +142,20 @@ class ImplementationName(StrEnum):
 class Variant(StrEnum):
     FREETHREADED = "freethreaded"
     DEBUG = "debug"
+    FREETHREADED_DEBUG = "freethreaded+debug"
+
+    @classmethod
+    def from_build_options(
+        cls: type["Variant"], build_options: list[str]
+    ) -> "Variant" | None:
+        if "debug" in build_options and "freethreaded" in build_options:
+            return cls.FREETHREADED_DEBUG
+        elif "debug" in build_options:
+            return cls.DEBUG
+        elif "freethreaded" in build_options:
+            return cls.FREETHREADED
+        else:
+            return None
 
 
 @dataclass
@@ -208,7 +222,10 @@ class CPythonFinder(Finder):
             cpython-
             (?P<ver>\d+\.\d+\.\d+(?:(?:a|b|rc)\d+)?)(?:\+\d+)?\+
             (?P<date>\d+)-
-            (?P<triple>[a-z\d_]+-[a-z\d]+(?>-[a-z\d]+)?-[a-z\d]+)-
+            # Note we lookahead to avoid matching "debug" as a triple as we'd
+            # prefer it matches as a build option; we could enumerate all known
+            # build options instead but this is the easy path forward
+            (?P<triple>[a-z\d_]+-[a-z\d]+(?>-[a-z\d]+)?-(?!debug(?:-|$))[a-z\d_]+)-
             (?:(?P<build_options>.+)-)?
             (?P<flavor>[a-z_]+)?
             \.tar\.(?:gz|zst)
@@ -377,13 +394,7 @@ class CPythonFinder(Finder):
         flavor = groups.get("flavor", "full")
 
         build_options = build_options.split("+") if build_options else []
-        variant: Variant | None
-        for variant in Variant:
-            if variant in build_options:
-                break
-        else:
-            variant = None
-
+        variant = Variant.from_build_options(build_options)
         version = Version.from_str(version)
         triple = self._normalize_triple(triple)
         if triple is None:
@@ -766,8 +777,10 @@ def render(downloads: list[PythonDownload]) -> None:
         match variant:
             case Variant.FREETHREADED:
                 return 1
-            case Variant.DEBUG:
+            case Variant.FREETHREADED_DEBUG:
                 return 2
+            case Variant.DEBUG:
+                return 3
         raise ValueError(f"Missing sort key implementation for variant: {variant}")
 
     def sort_key(download: PythonDownload) -> tuple: