Tests don't compile on non-Windows platforms

See https://github.com/microsoft/arcana.cpp/pull/49 which removed the tests.

Failure run: https://github.com/microsoft/arcana.cpp/actions/runs/18923881090

Capturing one here in case the build disappears. This is for macOS build.

/Users/runner/work/arcana.cpp/arcana.cpp/Source/Shared.Test/Threading/TaskUnitTest.cpp:1609:22: error: missing 'typename' prior to dependent type name 'expected_callable_traits<void, false, void, void, false, exception_ptr, basic_expected<void, exception_ptr>>::task_input_type'
 1609 |     EXPECT_EQ(typeid(ExpectedT::task_input_type).name(), typeid(ReceivedT::task_input_type).name());
      |                      ^~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from /Users/runner/work/arcana.cpp/arcana.cpp/Source/Shared.Test/Threading/TaskUnitTest.cpp:1:
** BUILD FAILED **
/Users/runner/work/arcana.cpp/arcana.cpp/Build/_deps/googletest-src/googletest/include/gtest/gtest.h:1869:63: note: expanded from macro 'EXPECT_EQ'

 1869 |   EXPECT_PRED_FORMAT2(::testing::internal::EqHelper::Compare, val1, val2)

      |                                                               ^~~~
The following build commands failed:
In file included from /Users/runner/work/arcana.cpp/arcana.cpp/Source/Shared.Test/Threading/TaskUnitTest.cpp:1:
	CompileC /Users/runner/work/arcana.cpp/arcana.cpp/Build/build/arcana_tests.build/Debug/Objects-normal/arm64/TaskUnitTest.o /Users/runner/work/arcana.cpp/arcana.cpp/Source/Shared.Test/Threading/TaskUnitTest.cpp normal arm64 c++ com.apple.compilers.llvm.clang.1_0.compiler (in target 'arcana_tests' from project 'arcana.cpp')
In file included from /Users/runner/work/arcana.cpp/arcana.cpp/Build/_deps/googletest-src/googletest/include/gtest/gtest.h:72:
(1 failure)
/Users/runner/work/arcana.cpp/arcana.cpp/Build/_deps/googletest-src/googletest/include/gtest/gtest_pred_impl.h:144:36: note: expanded from macro 'EXPECT_PRED_FORMAT2'
  144 |   GTEST_PRED_FORMAT2_(pred_format, v1, v2, GTEST_NONFATAL_FAILURE_)
      |                                    ^~
/Users/runner/work/arcana.cpp/arcana.cpp/Build/_deps/googletest-src/googletest/include/gtest/gtest_pred_impl.h:134:39: note: expanded from macro 'GTEST_PRED_FORMAT2_'
  134 |   GTEST_ASSERT_(pred_format(#v1, #v2, v1, v2), on_failure)
      |                                       ^~
/Users/runner/work/arcana.cpp/arcana.cpp/Build/_deps/googletest-src/googletest/include/gtest/gtest_pred_impl.h:79:52: note: expanded from macro 'GTEST_ASSERT_'
   79 |   if (const ::testing::AssertionResult gtest_ar = (expression)) \
      |                                                    ^~~~~~~~~~
/Users/runner/work/arcana.cpp/arcana.cpp/Source/Shared.Test/Threading/TaskUnitTest.cpp:1634:5: note: in instantiation of function template specialization 'ValidateCallableTraits<expected_callable_traits<void, false, void, void, false, std::exception_ptr, arcana::basic_expected<void, std::exception_ptr>>, arcana::internal::callable_traits<(lambda at /Users/runner/work/arcana.cpp/arcana.cpp/Source/Shared.Test/Threading/TaskUnitTest.cpp:1620:21), void>>' requested here
 1634 |     ValidateCallableTraits<expected, received>();
      |     ^

Start with Source/Shared.Test/Threading/TaskUnitTest.cpp around line 1609 and review the macOS failure from the linked GitHub Actions run. Check pull request #49 for context on the removed tests, then verify that the affected tests compile on non-Windows platforms and that the test build succeeds.