Match C GLOBAL_CODE repro assertions to failing Rust behavior

[zacharywhitley]

Motivation

• Reintroduce strict pre/post-drop verification in the C GLOBAL_CODE repro so it mirrors the stricter Rust repro checks and can reproduce the same lookup/unregistration failures.
• Ensure the C test exercises immediate and delayed drops across single-threaded, pressure, and threaded pressure scenarios with explicit mapped/unmapped assertions.

Description

• Added crates/c-api/tests/global_code.c helpers to obtain a module image start via wasmtime_module_image_range and to check /proc/self/maps for mapped/unmapped addresses.
• Inserted pre-drop assert_mapped and post-drop assert_unmapped checks around module lifetime in all repro paths, and recorded module_start for delayed-drop cases.
• Updated crates/c-api/tests/CMakeLists.txt to build and register test-global-code, and wrapped gtest setup behind the WASMTIME_CAPI_ENABLE_GTEST_TESTS option.

Testing

• Built the C API tests with cmake -S crates/c-api -B target/c-api-build-offline -DBUILD_TESTS=ON -DWASMTIME_CAPI_ENABLE_GTEST_TESTS=OFF && cmake --build target/c-api-build-offline --target test-global-code -j4, which completed successfully.
• Ran the repro test with ctest --test-dir target/c-api-build-offline -R test-global-code --output-on-failure, which reproduced the failing behavior (test run failed with threaded post-drop: expected unmapped address ...).

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