Fix lambda closure bug in concurrent plugin method execution

Replace inline lambda with named `materialize` helper to correctly
pass plugin method and arguments to the thread executor, preventing
all futures from calling the last plugin only.

beets/metadata_plugins.py

@@ -78,6 +78,12 @@ def _yield_from_plugins(
 ) -> Callable[..., Iterator[Ret]]:
     method_name = func.__name__
 
+    def materialize(
+        plugin: MetadataSourcePlugin, method_name: str, *args, **kwargs
+    ) -> list[Ret]:
+        method = getattr(plugin, method_name)
+        return list(method(*args, **kwargs))
+
     @wraps(func)
     def wrapper(*args, **kwargs) -> Iterator[Ret]:
         # Run plugin methods concurrently for faster I/O-bound lookups.
@@ -86,12 +92,9 @@ def _yield_from_plugins(
                 executor.submit(
                     # Evaluate iterator with list such that results are ready when
                     # future.result() is called.
-                    lambda *args, **kwargs: list(
-                        getattr(plugin, method_name)(
-                            *args,
-                            **kwargs,
-                        )
-                    ),
+                    materialize,
+                    plugin,
+                    method_name,
                     *args,
                     **kwargs,
                 ): plugin

docs/changelog.rst

@@ -59,6 +59,8 @@ Bug fixes
 - :doc:`plugins/discogs`: Prevent duplicate featured artists in track artist
   fields when the same artist is credited both in ``artists`` (for example with
   ``Feat.`` join text) and ``extraartists`` as ``Featuring``. :bug:`6166`
+- :ref:`import-cmd` Metadata source plugin ID lookups now correctly call each
+  plugin's own lookup method when running in parallel. :bug:`6583`
 
 ..
     For plugin developers

test/test_metadata_plugins.py

@@ -128,7 +128,6 @@ class TestSearchApiMetadataSourcePlugin(PluginMixin):
             search_plugin._search_api("track", "query", {})
 
 
-@pytest.mark.xfail(reason="Currently only the last plugin is called")
 def test_albums_for_ids_calls_each_plugin_once(monkeypatch):
     start_workers = Event()