Add optional timeout to Executor

[stefan-k]

Closes #332

• Timeout support in Executor
• Docs and Doctests
• Example
• Test
• 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 ⚠️

Additional details and impacted files

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

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.