fix: support custom slog levels

[lvlcn-t]

Motivation

Closes #116

Changes

I've removed the fromSlogLevel map and type casting to int32/Level instead.

For more information look at the commits.

Tests done

I've provided two unit tests with custom slog levels. If you want me to write additional test cases, feel free to ask for them.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 80.48%. Comparing base (2338a13) to head (5e028ac).
Report is 13 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #117      +/-   ##
==========================================
- Coverage   80.92%   80.48%   -0.44%     
==========================================
  Files          11       11              
  Lines         739      656      -83     
==========================================
- Hits          598      528      -70     
+ Misses        126      112      -14     
- Partials       15       16       +1     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[aymanbagabas]

Thank you @lvlcn-t!