Improve Swift type extraction coverage

[xbsjason]

Summary

• Index Swift protocol function requirements as methods.
• Capture Swift enum bodies as Enum nodes with the parent type name.
• Add regression coverage for Swift protocol, struct, and enum extraction.

Verification

• PASS: Swift extraction block from the C test runner after rebase. Confirmed swift_protocol, swift_struct, swift_enum, and Swift call extraction all pass.

Caveat

• make -f Makefile.cbm cbm currently fails on this machine in pre-existing production allocator code with unknown type name git_allocator when CBM_BIND_TS_ALLOCATOR=1.