Fix NCBI tests

[manulera]

• Add waiting time between tests
• Handle new response from entrez where 404 is not returned when requesting a wrong id, but instead a file with text, like the one below, from the url with wrong id

Error: F a i l e d  t o  u n d e r s t a n d  i d :  b l a h 

Example: https://eutils.ncbi.nlm.nih.gov/entrez/eutils/efetch.fcgi?db=nuccore&id=blah&rettype=gbwithparts&retmode=text

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.94%. Comparing base (ca71400) to head (d4c4fad).
⚠️ Report is 7 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #360      +/-   ##
==========================================
+ Coverage   96.91%   96.94%   +0.03%     
==========================================
  Files          27       27              
  Lines        2007     2031      +24     
==========================================
+ Hits         1945     1969      +24     
  Misses         62       62              

Flag	Coverage Δ
unittests	96.94% <100.00%> (+0.03%)	⬆️

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