Add memory tool call metrics to memories extension (#24583)

## Why

The memories extension now receives a metrics exporter, but the useful
extension-owned signal is the memory tool call itself: which operation
ran, which memory area it touched, whether the backend call succeeded,
and whether the result was truncated.

## What changed

- Added the `codex.memories.tool.call` counter in
`ext/memories/src/metrics.rs`.
- Emit that counter from `memories/add_ad_hoc_note`, `memories/list`,
`memories/read`, and `memories/search` after backend execution.
- Tag each call with `tool`, `operation`, `scope`, `status`, and
`truncated`.
- Pass the existing `MetricsClient` through the memories extension into
the tool executors; tests use `None`.

## Verification

- `just test -p codex-memories-extension`

codex-rs/ext/memories/src/tests.rs

@@ -415,10 +415,13 @@ async fn search_tool_rejects_legacy_single_query() {
 
 fn memory_tool(memory_root: &Path, tool_name: &str) -> Arc<dyn ToolExecutor<ToolCall>> {
     let expected_tool_name = memory_tool_name(tool_name);
-    crate::tools::memory_tools(LocalMemoriesBackend::from_memory_root(memory_root))
-        .into_iter()
-        .find(|tool| tool.tool_name() == expected_tool_name)
-        .unwrap_or_else(|| panic!("{tool_name} tool should be registered"))
+    crate::tools::memory_tools(
+        LocalMemoriesBackend::from_memory_root(memory_root),
+        /*metrics_client*/ None,
+    )
+    .into_iter()
+    .find(|tool| tool.tool_name() == expected_tool_name)
+    .unwrap_or_else(|| panic!("{tool_name} tool should be registered"))
 }
 
 fn memory_tool_name(tool_name: &str) -> ToolName {