[R21] Disambiguate generated receive events for overloaded messages

[JetF0x]

Addresses review finding R21.

Default RPC and broadcast overloads such as Update(int) and Update(string) previously emitted duplicate receive events and delegates. Qualify conflicting receive symbols with their existing signature-based message IDs, preserve single-method and explicit receive APIs, and retain inherited receive names, including interfaces in older compiled libraries. Document the subscription names in the README.

Validation: dotnet test Cat.Network.sln -c Release --no-restore --nologo passes all 250 tests (155 runtime, 53 analyzer, 42 generator), including 22 new overload cases that run the analyzer and generator together and dispatch both overloads to distinct handlers. The original regressions failed before the fix; wire IDs and explicit handlers remain unchanged.

Composition with #24: use ReceiveName for generated event/delegate/raise stems while retaining #24's escaped Identifier for send/explicit method names and its scoped local-name allocation.