fix(lsp): report incomplete rename and caller searches, make them cancellable (#472)

Rename and incoming calls open the project files that mention the name, like
Find Usages, but dropped the reason a search could miss usages and could not be
cancelled. A rename past the 300-file limit changed part of the usages without
saying so.

- Rename and call hierarchy return why the result may be incomplete and take a
  request id for cancel_request.
- A rename that may have missed usages always opens the preview, with a warning.
- The Callers tree shows the note above the tree or on the expanded node.
- Candidates too large or not readable as text are reported as skipped.
- A newer rename or hierarchy query cancels the one it replaces.

src/features/code-insight/HierarchyView.module.css

@@ -23,6 +23,13 @@
   margin: 0 4px;
   background: var(--border);
 }
+.note {
+  flex: none;
+  padding: 0 8px 4px;
+  font-size: var(--fs-small);
+  font-style: italic;
+  color: var(--fg-subtle);
+}
 .body {
   flex: 1;
   min-height: 0;