Improve error message when temporary folder cannot be safely determined

[robomics]

This PR introduces three changes:

• Improve the error message issued by hictk when the path to a temporary directory cannot be safely determined
• In case of errors, check whether the HICTK_CI env variable is defined - this is used to workaround known issues with tmp folders in the CI environment
• Avoid raising errors when there are issues with the tmpdir detection, and this clearly won't lead to any issues (e.g. when calling hictk --help)

Closes #193

[codecov]

Codecov Report

Attention: Patch coverage is 83.33333% with 3 lines in your changes missing coverage. Please review.

Project coverage is 85.12%. Comparing base (48341b4) to head (f41e476).
Report is 29 commits behind head on main.

Files	Patch %	Lines
src/hictk/cli/cli_balance.cpp	66.66%	2 Missing ⚠️
src/hictk/cli/cli_load.cpp	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #210      +/-   ##
==========================================
+ Coverage   85.10%   85.12%   +0.02%     
==========================================
  Files         120      120              
  Lines       10332    10355      +23     
==========================================
+ Hits         8793     8815      +22     
- Misses       1539     1540       +1     

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[paulmenzel]

Feel free to squash my commit. No need to mention. ;-)