Add configurable backup snapshot fetching from primary

[Copilot]

• Add backup snapshot fetch feature with BackupSnapshotFetch task, snapshot evidence hook, config plumbing, and e2e test
• Remove max_size from backup snapshot fetch configuration
• Add target_rpc_interface config to backup snapshot fetch
• Fix C++ formatting (clang-format) in configuration.h and node_state.h

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[achamayou]

@copilot drop the max_size constraint and configuration, it is not necessary here.

[Copilot]

@copilot drop the max_size constraint and configuration, it is not necessary here.

Removed max_size from the BackupFetch config struct, JSON serialization, config schema, and CHANGELOG. The underlying fetch_from_peer call now uses std::numeric_limits<size_t>::max() instead. Done in 3b9c163.

[achamayou]

@copilot ok actually we need one more thing in the configuration here: the name of the rpc_interface to use on the target node to download the snapshot. That has to be used when grabbing the network details of the primary from the KK to attempt the fetch from it in the BackupSnapshotFetch task. We can't just take the first interface, it may not have the SnapshotRead feature enabled on it.

[Copilot]

@copilot ok actually we need one more thing in the configuration here: the name of the rpc_interface to use on the target node to download the snapshot. That has to be used when grabbi...

Added target_rpc_interface field to BackupFetch config (default: "primary_rpc_interface"). The BackupSnapshotFetch task now looks up the primary's interface by this configured name via rpc_interfaces.find() instead of using the first available interface. Done in 388c734.

[achamayou]

@copilot run ./scripts/ci-checks.sh -f to format the code

[Copilot]

@copilot run ./scripts/ci-checks.sh -f to format the code

Fixed C++ formatting in configuration.h (multi-line macro args) and node_state.h (line length). Python files were already clean. Done in df810b9.