[Master-Chiken]

Closes #31

Adds one machine-readable // metadata comment before each section entry in generated splits.txt files.

• Executables include the zero-based decomp-toolkit section index, original ELF section index, absolute address, and size.
• RELs include both section indices, size, module ID, and the virtual address when one is available; no absolute address is emitted for relocatable sections.
• The existing parser already ignores standalone // comment lines, so this format is intended to remain backward compatible.
• Adds unit tests for executable metadata, REL metadata, and parser compatibility.

Draft while CI and the exact metadata schema are reviewed.