Fix too many open files on file system

[quambene]

Fix too many open files on file system:

• Set the default for max_idle_connections_per_host in settings.json from 100 to the more sensible 10. Idle connections were stuck in the connection pool.
• Idle connections will be removed after 5 seconds (see idle_connections_timeout in settings.json).

[codecov]

Codecov Report

Attention: 6 lines in your changes are missing coverage. Please review.

Comparison is base (9a6ff33) 90.63% compared to head (7ac66c5) 90.55%.

Files	Patch %	Lines
src/cmd/fetch.rs	0.00%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #62      +/-   ##
==========================================
- Coverage   90.63%   90.55%   -0.09%     
==========================================
  Files          31       31              
  Lines        4059     4064       +5     
==========================================
+ Hits         3679     3680       +1     
- Misses        380      384       +4     

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