Deal with base count misplaced

[manulera]

Temp fix waiting for biopython/biopython#5173

---

Note

Medium Risk
Changes GenBank parsing behavior by pre-filtering input lines, which could mask malformed files or subtly alter downstream parsing; impact is limited to genbank imports and covered by a new regression test.

Overview
Adds a temporary workaround in custom_file_parser for GenBank files by stripping any BASE COUNT lines (even if misplaced) before running Bio.SeqIO.parse, avoiding Biopython parsing failures.

Adds a regression test and fixture (base_count_misplaced.gb) to ensure such files can be parsed successfully.

^{Written by Cursor Bugbot for commit 1d71d81. This will update automatically on new commits. Configure here.}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.03%. Comparing base (4a00fef) to head (1d71d81).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #410   +/-   ##
=======================================
  Coverage   97.03%   97.03%           
=======================================
  Files          31       31           
  Lines        1953     1959    +6     
=======================================
+ Hits         1895     1901    +6     
  Misses         58       58           

Flag	Coverage Δ
unittests	97.03% <100.00%> (+<0.01%)	⬆️

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