Better messaging for alerts unavailability

[albireox]

Fixes #54

[codecov]

Codecov Report

❌ Patch coverage is 19.44444% with 29 lines in your changes missing coverage. Please review.
✅ Project coverage is 27.51%. Comparing base (2c08351) to head (3406b2e).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
src/gort/overwatcher/alerts.py	23.80%	16 Missing ⚠️
src/gort/overwatcher/overwatcher.py	0.00%	8 Missing ⚠️
src/gort/tools.py	20.00%	4 Missing ⚠️
src/gort/devices/guider.py	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #55      +/-   ##
==========================================
- Coverage   27.51%   27.51%   -0.01%     
==========================================
  Files          39       39              
  Lines        6897     6910      +13     
  Branches     1094     1095       +1     
==========================================
+ Hits         1898     1901       +3     
- Misses       4980     4989       +9     
- Partials       19       20       +1     

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