feat(ffi): add standalone ffi package

[JP-Ellis]

📝 Summary

Separate out the FFI from the core Pact Python library.

🚨 Breaking Changes

The pact.v3.ffi module is replaced by the pact_ffi package. The old module will alias the new one, so there will not be a breaking change for now; however, it is advised to replace pact.v3.ffi.{function} with the corresponding pact_ffi.{function} as the former will be removed in later versions.

🔥 Motivation

To decouple the releases of FFIs from the core Pact Python functionality.

🔨 Test Plan

CI

🔗 Related issues/PRs

• Separate Pact Python CLI and FFI #1082

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 69%. Comparing base (a3dfbda) to head (ed64107).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@          Coverage Diff           @@
##           main   #1129     +/-   ##
======================================
- Coverage    78%     69%     -9%     
======================================
  Files        32      33      +1     
  Lines      3728    5012   +1284     
======================================
+ Hits       2942    3506    +564     
- Misses      786    1506    +720     

Flag	Coverage Δ
examples	58% <ø> (ø)
tests	69% <ø> (-9%)	⬇️

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