Rollup merge of #144308 - GuillaumeGomez:merged-doctest-times, r=lolbinarycat

[rustdoc] Display total time and compilation time of merged doctests

Fixes rust-lang/rust#144270.

Does it look good to you `@kpreid?`

<img width="908" height="263" alt="image" src="https://github.com/user-attachments/assets/cd5d082d-c4e0-42ed-91dd-bd263b413dcd" />

Author: samueltardieu