Add `sources` action to `stdump` for smoother `uncc` workflows

[PerikiyoXD]

Summary

Right now, generating a SOURCES.TXT with stdump files requires some manual cleanup—like trimming offsets and fixing up paths (e.g., making them relative). It feels like the tool could handle this by default to avoid extra work.

This is mostly about making the workflow painlessly fluent—where the generated files are ready to use with minimal extra steps.

What's the issue

• SOURCES.TXT ends up with absolute paths that you have to manually fix.
• The offsets in the output need trimming to work properly with uncc, as explained by the README.
• Having to do these manual tweaks preemptively adds friction, especially when you'd expect the generated file to just work out of the box.

What could improve

• Add a dedicated high-level action sources to stdump:
  stdump sources my.elf -o my_elf_output/
  Which would directly output a SOURCES.TXT formatted file, properly trimmed and ready to use with uncc.

Example of expected workflow

stdump sources my.elf -o my_elf_output/
uncc my.elf my_elf_output/

This would make the purpose of each action clear, while keeping the workflow simple and predictable.