docs: add usage examples to README

[bdraco]

Summary

• Add usage examples covering the main public API: GAP advertisement parsing, address utilities, distance estimation, monotonic time, and private address resolution
• Helps new users quickly understand how to use the library

Test plan

• Verify README renders correctly on GitHub

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (7bf5546) to head (d30e5a3).
⚠️ Report is 98 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #200   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files            6         6           
  Lines          255       255           
  Branches        38        38           
=========================================
  Hits           255       255           

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[codspeed-hq]

Merging this PR will not alter performance

✅ 9 untouched benchmarks

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_{Comparing add-readme-usage-docs (d30e5a3) with main (7bf5546)}