Add optional timeout to `Executor`

[stefan-k]

Closes #332

• [x] Timeout support in Executor
• [x] Docs and Doctests
• [x] Example
• [x] Test
• [x] Mention in book (?)

[codecov-commenter]

Codecov Report

Attention: 3 lines in your changes are missing coverage. Please review.

Comparison is base (b74620c) 90.26% compared to head (9be41c9) 90.27%.

Files	Patch %	Lines
argmin/src/core/executor.rs	91.66%	3 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #405 +/- ## ======================================= Coverage 90.26% 90.27% ======================================= Files 141 141 Lines 19906 19947 +41 ======================================= + Hits 17969 18007 +38 - Misses 1937 1940 +3 ```

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