I want to refactor the existing time detail handling in the codebase. Specifically, I'd like to replace the `write_time_detail` function with a new `merge_time_detail` function, which will add new time details to the existing ones rather than overwriting them. This change should be applied across the codebase wherever `write_time_detail` is used, including in `src/coprocessor/endpoint.rs`, `src/server/service/kv.rs`, `src/storage/txn/tracker.rs`, and any related test cases. Please ensure that all occurrences of the old function are updated to use the new one. Additionally, add a test to validate that the `process_wall_time_ns` is correctly merged and is not zero, which will ensure the merging is functioning as intended. Make sure these changes preserve backward compatibility and do not introduce any regressions in functionality.