Add Path equality for new compiler

[lukewilliamboswell]

Summary

• opt opaque Path into compiler-derived is_eq support required by the new compiler
• derive equality structurally from the exact tagged UTF-8, Unix-byte, or Windows-unit representation

Validation

• ci/all_tests.sh
  • format check
  • package check and 71 tests
  • docs generation
  • bundle generation
  • bundled example check, test, run, build, and execution