Replace imio with brainglobe-utils

[IgorTatarnikov]

imio was still being used in the brainmapper tests. Replaced this with the appropriate brainglobe-utils function.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 85.83%. Comparing base (dbec4e9) to head (3290b15).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #128   +/-   ##
=======================================
  Coverage   85.83%   85.83%           
=======================================
  Files          17       17           
  Lines         847      847           
=======================================
  Hits          727      727           
  Misses        120      120           

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