Show action duration in explorer panel

**Is your feature request related to a problem? Please describe.**

I need to go to the Web UI in order to see how actions perform.

**Describe the solution you'd like**

Show duration of the action and step in human readable format on the right.

**Additional context**


Start by locating the explorer panel's rendering of actions and steps, then check whether duration data is already available from the existing action details. Add human-readable durations for both levels on the right and verify the displayed values against the Web UI or existing extension behavior.

索引モデルが issue の本文から書いたものです。