CI: isolate re-init-heavy embed fixtures; drop obsolete TestDomainReload

CPython 3.13+ does not fully support repeated Py_Finalize/Py_Initialize.
The embed-test suite re-initializes the interpreter per fixture (~40 cycles
in one process); on 3.13/3.14 the accumulation eventually corrupts
interpreter state and a later Py_Initialize aborts with "Failed to import
encodings module" (strace confirms the file opens fine - it is interpreter
state, not the filesystem). The crash point is nondeterministic and only
appears in the full suite; each fixture passes in isolation.

Run the re-init-heavy fixtures (TestPythonEngineProperties, pyinitialize,
TestFinalizer) in a separate test process so no single process accumulates
enough re-inits to corrupt. This mirrors upstream's NeedsReinit separation.

TestDomainReload is excluded entirely: AppDomain reload is not supported on
modern .NET (single-domain), so those tests are obsolete.

Verified locally: full embed suite green on 3.11, 3.13 and 3.14 with the
split (bulk 895-896 / re-init batch 14, 0 failures); no regression.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: Martin-Molinero

.github/workflows/main.yml

@@ -48,8 +48,18 @@ jobs:
           echo PYTHONNET_PYDLL=$(python -m pythonnet.find_libpython) >> $GITHUB_ENV
           echo PYTHONHOME=$(python -c 'import sys; print(sys.prefix)') >> $GITHUB_ENV
 
+      # The fixtures that repeatedly tear down and re-initialize the interpreter
+      # (TestPythonEngineProperties / pyinitialize / TestFinalizer) are run in a separate
+      # process. CPython 3.13+ does not fully support repeated Py_Finalize/Py_Initialize:
+      # accumulating ~40 per-fixture re-inits in one process eventually corrupts interpreter
+      # state ("Failed to import encodings module"). Isolating the re-init-heavy fixtures
+      # keeps each process's accumulation low. TestDomainReload is excluded entirely:
+      # AppDomain reload is not supported on modern .NET (single-domain), so it is obsolete.
       - name: Embedding tests
-        run: dotnet test --runtime any-x64 --logger "console;verbosity=detailed" src/embed_tests/
+        run: dotnet test --runtime any-x64 --logger "console;verbosity=detailed" src/embed_tests/ --filter "FullyQualifiedName!~TestPythonEngineProperties&FullyQualifiedName!~pyinitialize&FullyQualifiedName!~TestFinalizer&FullyQualifiedName!~TestDomainReload"
+
+      - name: Embedding tests (re-initialization fixtures, isolated process)
+        run: dotnet test --runtime any-x64 --logger "console;verbosity=detailed" src/embed_tests/ --filter "FullyQualifiedName~TestPythonEngineProperties|FullyQualifiedName~pyinitialize|FullyQualifiedName~TestFinalizer"
 
       - name: Python Tests (.NET Core)
         run: pytest --runtime netcore tests