Add ADR for command-line option handling best practices

[tautschnig]

Add comprehensive documentation for command-line option handling best practices based on GitHub issue #1521. Includes philosophy, architecture, and step-by-step developer guide.

Fixes: #1521

• Each commit message has a non-empty body, explaining why the change was made.
• n/a Methods or procedures I have added are documented, following the guidelines provided in CODING_STANDARD.md.
• n/a The feature or user visible behaviour I have added or modified has been documented in the User Guide in doc/cprover-manual/
• n/a Regression or unit tests are included, or existing tests cover the modified code (in this case I have detailed which ones those are in the commit message).
• n/a My commit message includes data points confirming performance improvements (if claimed).
• My PR is restricted to a single feature or bugfix.
• n/a White-space or formatting changes outside the feature-related changed lines are in commits of their own.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.00%. Comparing base (1505c36) to head (affa974).

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #8758   +/-   ##
========================================
  Coverage    80.00%   80.00%           
========================================
  Files         1700     1700           
  Lines       188254   188254           
  Branches        73       73           
========================================
  Hits        150615   150615           
  Misses       37639    37639           

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