fix: support PEP 810 global lazy imports

[JP-Ellis]

✈️ Pre-flight checklist

• I have read the Contributing Guidelines on pull requests.
• If this is a code change: I have written unit tests and/or added dogfooding pages to fully verify the new behavior.
• If this is a new API or substantial change: the PR has an accompanying issue (closes #0000) and the maintainers have approved on my working plan.

📝 Summary

On Python 3.15, Pact breaks for users who turn on PEP 810 lazy imports globally with PYTHON_LAZY_IMPORTS=all or -X lazy_imports=all. Three attributes resolve to the wrong value:

Attribute	Under lazy_imports=all	Cause
pact_ffi.ffi	the pact_ffi.ffi extension module, so the first FFI call raises AttributeError: module 'pact_ffi.ffi' has no attribute 'NULL'	The submodule shares the attribute's name
pact.__version__, pact_ffi.__version__	the __version__ submodule, whenever __version_tuple__ is read first	The submodule shares the attribute's name
pact.match, pact.generate	AttributeError	Only bound as a side effect of pact.xml importing them

The name collisions. from pact_ffi.ffi import ffi binds ffi lazily. When the submodule loads later, the import system sets the package attribute ffi to the module, replacing the object. Each package now imports the colliding submodule under an alias and assigns the attribute from it, so the binding happens after the submodule has loaded.

The missing attributes. pact/__init__.py now imports match and generate explicitly. Without lazy imports, both were already imported, so this adds no cost.

The pact_ffi fix reaches users with the next pact-python-ffi release.

🔥 Motivation

PEP 810 makes global lazy mode a user choice, so pact should work under it.

🔨 Test Plan

• tests/test_lazy_imports.py runs on Python 3.15 and is skipped on older versions. In a subprocess with -X lazy_imports=all, it checks that each public attribute keeps its type, reading __version_tuple__ first. It also checks that an FFI call works.
• pytest itself cannot run under PYTHON_LAZY_IMPORTS=all: its lazily imported fnmatch raises ImportCycleError. Setting PACT_TEST_LAZY_IMPORTS=1 instead makes tests/conftest.py lazy-load only the imports issued by pact and pact_ffi modules. A new CI step runs the suite that way on Python 3.15, Linux only.
• Locally on Python 3.15:
  • Normal mode: the core and FFI suites pass, 558 passed and 14 skipped.
  • Lazy-import mode (PACT_TEST_LAZY_IMPORTS=1): the suite passes, 536 passed and 14 skipped.
  • Lazy-import mode on main: the same run gives 146 failures in tests/test_pact.py alone, and the new regression tests fail 6 of 8.

🔗 Related issues/PRs

Merges independently of #1734; the two branches touch no common files.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 68%. Comparing base (a225d82) to head (f0424d8).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@         Coverage Diff          @@
##           main   #1735   +/-   ##
====================================
  Coverage    68%     68%           
====================================
  Files        20      20           
  Lines      3288    3295    +7     
====================================
+ Hits       2261    2268    +7     
  Misses     1027    1027           

Flag	Coverage Δ
examples	52% <100%> (+<1%)	⬆️
tests	67% <100%> (+<1%)	⬆️

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