Neighbourhood signal broadcast loopback

[lucksus]

Fixes #567

1. Added the loopback parameter to the GraphQL mutation definitions in MutationDefinitions.ts
2. Updated the Rust mutation resolvers in mutation_resolvers.rs to handle the loopback parameter for both neighbourhoodSendBroadcast and neighbourhoodSendBroadcastU
3. Implemented the loopback functionality in the NeighbourhoodController's send_broadcast method, which now processes the broadcast locally when loopback is enabled
4. Updated the TypeScript resolver definitions in NeighbourhoodResolver.ts to include the loopback parameter

The implementation ensures that when loopback is enabled:

1. The broadcast is sent to all connected agents as usual
2. The broadcast is also processed locally through the signal handler for the same perspective
   This allows the same agent to receive their own broadcasts when needed, which is crucial for multi-device syncing