Internal environment variable handling and documentation

[BrianMichell]

Currently the internal MDIO API leverages multiple environment variables for different runtime configuration options. The getters for all of these configurations are all scattered, leverage raw os.environ calls, have differing levels of validation, and possibly rely on opaque defaults.

This PR seeks to create a unified repository of runtime configuration options for enhanced clarity and documentation.

New documentation page

[codecov]

Codecov Report

❌ Patch coverage is 94.64286% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 87.23%. Comparing base (c3ba558) to head (be2eae5).
⚠️ Report is 206 commits behind head on main.

Files with missing lines	Patch %	Lines
src/mdio/segy/_workers.py	33.33%	2 Missing ⚠️
src/mdio/converters/segy.py	90.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #730      +/-   ##
==========================================
+ Coverage   85.30%   87.23%   +1.92%     
==========================================
  Files          46       88      +42     
  Lines        2219     4826    +2607     
  Branches      306      318      +12     
==========================================
+ Hits         1893     4210    +2317     
- Misses        281      544     +263     
- Partials       45       72      +27     

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