Clarify fixture navigation and avoid a test handle clone

Summary:
Document why module fixtures are checked before the lazy conftest walk. Borrow the existing conftest handle when constructing its indexing request, removing the clone-to-slice lint.

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landed-with-radar-review

Differential Revision: D129106475

fbshipit-source-id: 7fd53304179a4e70dd89fe8465210e559fdfd5d0

Author: stroxler

pyrefly/lib/state/lsp/pytest.rs

@@ -122,6 +122,7 @@ impl<'a> Transaction<'a> {
             })
             .collect();
         if definitions.is_empty() && preference.follow_pytest_conftest {
+            // Module fixtures take precedence; discover conftests only after a local miss.
             let candidates = once(handle.clone())
                 .chain(once_with(|| pytest_conftest_handles(self, handle, preference)).flatten());
             'fixtures: for fixture_handle in candidates {

pyrefly/lib/test/lsp/definition.rs

@@ -482,7 +482,7 @@ def test_thing(answer):
     let mut transaction = state.new_committable_transaction(Require::Indexing, None);
     transaction
         .as_mut()
-        .run(&[conftest_handle.clone()], Require::Indexing, None);
+        .run(slice::from_ref(&conftest_handle), Require::Indexing, None);
     state.commit_transaction(transaction, None);
     let transaction = state.transaction();
     assert!(transaction.get_ast(&conftest_handle).is_none());