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.

Related issue

• Related to Swift: CALLS edges not resolved — hotspots, clusters, boundaries empty #43 for Swift language extraction/call-graph coverage.

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.

[DeusData]

Huge thanks for opening this PR and for the work you put into it.

The maintainer shop is currently full, so this may sit for a bit before it gets a proper review. We will come back to this as soon as possible with real feedback; I wanted to make sure it did not sit unacknowledged in the meantime.

[DeusData]

Thanks for improving Swift extraction coverage. Before review can continue, please add a DCO Signed-off-by trailer to the non-merge commit and link the language coverage issue if there is one.