Trace tool call receipt, result readiness, and code-mode dispatch (#44661)

## Why

Tool results can be ready before the sampling loop collects them, and code-mode cells can outlive a turn. Separate trace milestones make these timings visible and link nested calls to the turn that dispatches them.

## What changed

- Emit `codex.tool_call_received` and `codex.tool_result_ready` events for direct and code-mode calls, using identifiers and tool names without arguments or output. Record readiness before result encoding or collection, including ordinary errors and aborted responses, but excluding fatal errors.
- Assign nested call IDs at broker receipt and carry them through dispatch. Trace dispatch and interruptions caused by cancellation, cell closure, or abandonment.
- Add code-mode execute and wait handler spans with conversation, turn, call, and cell identifiers and `completed`, `failed`, or `interrupted` outcomes.

GitOrigin-RevId: b098a29d8ee030c823665e4b1031a0d67cc09502

codex-rs/core/src/session/session.rs

@@ -1577,6 +1577,7 @@ impl Session {
                 ),
                 executed_tool_calls: executed_tool_calls.clone(),
                 code_mode_service: crate::tools::code_mode::CodeModeService::new(
+                    thread_id,
                     Arc::clone(&code_mode_session_provider),
                     &config.code_mode,
                     executed_tool_calls,

codex-rs/core/src/session/tests.rs

@@ -6718,6 +6718,7 @@ pub(crate) async fn make_session_and_context() -> (Session, TurnContext) {
         ),
         executed_tool_calls: executed_tool_calls.clone(),
         code_mode_service: crate::tools::code_mode::CodeModeService::new(
+            thread_id,
             Arc::new(codex_code_mode::DisabledCodeModeSessionProvider),
             &config.code_mode,
             executed_tool_calls,
@@ -8891,6 +8892,7 @@ where
         ),
         executed_tool_calls: executed_tool_calls.clone(),
         code_mode_service: crate::tools::code_mode::CodeModeService::new(
+            thread_id,
             Arc::new(codex_code_mode::DisabledCodeModeSessionProvider),
             &config.code_mode,
             executed_tool_calls,