docs: Update README benchmarks

[ciscorn]

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[Copilot]

Pull request overview

Updates the repository README to reflect current project naming and refresh the published benchmark numbers for the Rust implementation vs. earcut.hpp.

Changes:

• Renames the README title to “earcut (Rust)”.
• Updates the benchmarks section: clarifies “time per iteration” and refreshes the table values.
• Removes the earcutr comparison and updates the accompanying note.

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[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.73%. Comparing base (9536527) to head (6d48555).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #42   +/-   ##
=======================================
  Coverage   99.73%   99.73%           
=======================================
  Files           3        3           
  Lines        1859     1859           
=======================================
  Hits         1854     1854           
  Misses          5        5           

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