Add a test app that verifies PLACE_IN_SECTION, _SECTION_ATTR_SYMBOL_DECL_GENERIC,
_SECTION_START and _SECTION_END macros work correctly on Linux.
The test places 5 uint32_t values into a custom .test_data_table section from
two separate translation units, then iterates the section at runtime to verify
the correct count and content of all entries.
Includes:
- Custom linker script (ld/test_section.ld)
- Build-test-rules entry (linux only)
- pytest host_test marker
