chore: Stop populating NetworkTopology::full_topology

[alin-at-dfinity]

NetworkTopology::full_topology (only populated for the NNS subnet) holds the same subnets as NetworkTopology::subnets and the same routing table as NetworkTopology::routing_table. Stop populating it, so it can be dropped in a future release.

[zeropath-ai]

✅ No security or compliance issues detected. Reviewed everything up to 7864311.

Security Overview

• 🔎 Scanned files: 5 changed file(s)
• 🔗 Scan Link: https://zeropath.com/app/repositories/f5e9d2bb-29a4-4b64-902a-391d65fd8b2d?scanId=e55c6423-9934-4ff4-b043-d7a76912a7b8&codeScanTypes=PrScan&tab=issues

Detected Code Changes

Change Type	Relevant files
Refactor	► rs/messaging/src/message_routing.rs     Rename variable all_subnets to subnets and adjust related logic ► rs/messaging/src/message_routing.rs     Remove full_topology construction for non-NNS paths and set None instead
Refactor	► rs/messaging/src/message_routing.rs     Update usage of routing_table variable name from full_routing_table to routing_table ► rs/messaging/src/message_routing.rs     Drop construction of full_topology for non-NNS subnets
Refactor	► rs/messaging/src/message_routing.rs     Update NetworkTopology creation to pass None for full_topology
Refactor	► rs/messaging/src/message_routing/tests.rs     Import NetworkTopologyTesting and adjust tests to reflect topology accessors behavior ► rs/messaging/src/message_routing/tests.rs     Replace previous tests with new approach for full_topology handling across subnets
Refactor	► rs/replicated_state/src/lib.rs     Adjust re-exports to remove FullTopology from public path in this file
Refactor	► rs/replicated_state/src/metadata_state.rs     Expose full_topology in testing trait and implement accessor ► rs/replicated_state/src/metadata_state.rs     Add full_topology getter to testing implementation
Refactor	► rs/replicated_state/src/metadata_state/tests.rs     Update tests for routing topology to reflect new full_topology related behavior and recent API changes