Add per-tool timing and performance breakdown

[saibotma]

It would be useful to have a simple performance view that shows where an agent run spent its time, especially the duration of each individual tool call.

I know there have already been requests for per-turn stats and improved tool-call rendering (#2518, #3853), but I’m specifically interested in using the timing data to find performance bottlenecks.

For example, being able to sort tool calls by duration would make it easy to identify slow commands, tests, searches, MCP calls, etc. and optimize them.

Ideally it would also show total model/provider time vs. tool execution time, and distinguish actual tool execution from T3 Code/orchestration overhead where possible.