Add Close() method to logger

[treyburn]

• Add a Close() method to the Logger interface
• Basic implementation for both File and Postgres loggers
• Added synctest for File logger to ensure we don't leak any goroutines.

[codecov]

Codecov Report

❌ Patch coverage is 50.00000% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 33.07%. Comparing base (f6428ab) to head (bea1490).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
internal/pkg/logger/postgres.go	0.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #18      +/-   ##
==========================================
+ Coverage   32.68%   33.07%   +0.39%     
==========================================
  Files           5        5              
  Lines         257      263       +6     
==========================================
+ Hits           84       87       +3     
- Misses        170      173       +3     
  Partials        3        3              

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