Disable snapshot read endpoints by-default, require a per-interface opt-in to enable new OperatorFeature

[eddyashton]

This has a bunch of knock-on effects. The related diffs may not all be strictly required, I've lost track, but they lead to a cleaner API (for things like "create a new node" in the Python infra) and I think for backporting purposes they all land together.

[Copilot]

Pull Request Overview

This PR refactors the network interface configuration system and adds opt-in feature gating for snapshot-serving endpoints to prevent public DoS attacks. The changes introduce a new FILE_SERVING_RPC_INTERFACE with FileAccess feature enabled by default, and modify the test infrastructure to use a more fluent API pattern for configuring nodes.

Key changes:

• Introduces opt-in feature gating for endpoints, specifically for file access/snapshot serving
• Refactors RPCInterface.from_args() to apply_args() and adds HostSpec.with_args() for better composability
• Adds a dedicated file-serving interface to all nodes by default with FileAccess feature enabled
• Moves snapshot-serving handlers from node_frontend.h to new file_serving_handlers.h file

Reviewed Changes

Copilot reviewed 32 out of 32 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
tests/infra/interfaces.py	Refactors interface configuration with apply_args() and with_args() methods, adds FILE_SERVING_RPC_INTERFACE
tests/infra/e2e_args.py	Simplifies nodes() function to use HostSpec.with_args()
tests/infra/node.py	Improves interface lookup with error handling
tests/infra/network.py	Updates create_node() to accept optional host parameter
tests/e2e_operations.py	Updates snapshot access tests to use FILE_SERVING_RPC_INTERFACE
src/node/rpc/file_serving_handlers.h	New file containing extracted snapshot-serving handlers with feature gating
src/node/rpc/frontend.h	Adds feature checking logic for endpoints
src/endpoints/endpoint.cpp	Adds require_optin_feature() method
include/ccf/endpoint.h	Defines OptInFeatures and adds required_optin_features field
doc/host_config_schema/cchost_config.json	Documents enabled_optin_features configuration option

Comments suppressed due to low confidence (1)

tests/infra/basicperf.py:213

• Call to function nodes with too few arguments; should be no fewer than 2.

    hosts = args.nodes or infra.e2e_args.nodes(1)