fix(core): Typing in auth

[Tranquility2]

Lets try and continue the journey from #305
(the goal is to get core marked as typed)

poetry run mypy --config-file pyproject.toml core/tests/test_auth.py core/testcontainers/core/auth.py
Success: no issues found in 2 source files

[codecov]

Codecov Report

Attention: Patch coverage is 75.00000% with 2 lines in your changes missing coverage. Please review.

Please upload report for BASE (main@2cf5a9f). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
core/testcontainers/core/auth.py	75.00%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #691   +/-   ##
=======================================
  Coverage        ?   77.81%           
=======================================
  Files           ?       12           
  Lines           ?      604           
  Branches        ?       90           
=======================================
  Hits            ?      470           
  Misses          ?      107           
  Partials        ?       27           

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[Tranquility2]

I know #504 also exists but I feel we need to make it into smaller iteration to get the a goal, treating each core component as a milestone doesn't mean it will all be perfect (time and other commits are bound to make a mess) but it should allow us to get much closer so that the the last mile will be much simpler.