Fix Swift generator naming collisions

[tolgahan-arikan]

Summary

• make generated Swift enum fallback cases collision-aware, preserving schema cases such as .unknown and using a separate associated-value fallback for unrecognized wire values
• add bounded numeric fallback names for exhausted enum and method namespace collisions, with explicit template failures instead of emitting blank or invalid Swift
• emit raw-value-free empty CodingKeys enums so structs and method wrappers with no exported fields compile
• make generated method namespaces collision-aware when a method name shadows a top-level type, while preserving the public client method name and RPC path
• add Swift compile-backed regression tests for enum fallback collisions, empty coding keys, and method/type naming collisions

Trails API verification

Verified against ../trails-api/proto/trails-api.ridl with -service=Trails -methodTreeShake -ignore=@onramp. Fresh Swift output:

• keeps public func runtimeStatus() as the client method
• preserves /rpc/Trails/RuntimeStatus as the wire path
• uses TrailsApiTrailsAPI.RuntimeStatusMethod for the nested method namespace, avoiding the top-level RuntimeStatus DTO collision
• uses .unknownValue(String) for enums in that schema that already define UNKNOWN
• emits enum CodingKeys: CodingKey for empty generated request/response structs

Test Plan

• go test ./...
• ./Tests/test.sh
• go -C tools tool webrpc-gen -schema=../../trails-api/proto/trails-api.ridl -target=.. -client -service=Trails -methodTreeShake -ignore=@onramp -out=/tmp/trails-relative.gen.swift
• swiftc -parse-as-library -target arm64-apple-macosx12.0 -c /tmp/trails-relative.gen.swift -o /tmp/trails-relative.gen.o
• rg -n '(/Users/|manual|FIXME|TODO|RuntimeStatusMethod|enum CodingKeys: CodingKey|unknownValue)' /tmp/trails-relative.gen.swift

[VojtechVitek]

LGTM.

Can you regenerate the examples and potentially add some unit tests (with Claude)?