Revise README to clarify usage, pytest patterns, and debug/debugging behavior

[Code0x58]

Motivation

• Make the README clearer and friendlier for new users by explicitly describing the library's purpose and workflow.
• Surface common pytest usage patterns and examples so users can more easily run equivalence and benchmark tests.
• Improve explanations of safety guarantees and debug behavior so users understand runtime and registration constraints.

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Codex Task

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (44f25f8) to head (2f6c62a).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff            @@
##            master       #11   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            1         1           
  Lines          194       194           
=========================================
  Hits           194       194           

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