feat: ic0_subnet_self_node_count

[eichhorl]

Implement a new system API function allowing a canister to determine the size of its current subnet. This will be helpful for flexible outcalls, in which a canister can individually specify how many replicas should perform a request, and how many of them should produce a response. This only makes sense within the context of the own subnet size.

Specified here (draft): dfinity/developer-docs#254

[zeropath-ai]

✅ No security or compliance issues detected. Reviewed everything up to 45d660d.

Security Overview

• 🔎 Scanned files: 10 changed file(s)
• 🔗 Scan Link: https://zeropath.com/app/repositories/f5e9d2bb-29a4-4b64-902a-391d65fd8b2d?scanId=6576f4c1-7e06-4ed1-a43a-762357a815b6&codeScanTypes=PrScan&tab=issues

Detected Code Changes

Change Type	Relevant files
Enhancement	► rs/embedders/src/wasm_utils/validation.rs     Add subnet_self_node_count system API entry point
Enhancement	► rs/embedders/src/wasmtime_embedder/linker.rs     Wrap ic0.subnet_self_node_count in linker module
Enhancement	► rs/embedders/src/wasmtime_embedder/system_api.rs     Implement ic0_subnet_self_node_count API method
Enhancement	► rs/embedders/src/wasmtime_embedder/system_api_complexity.rs     Add SUBNET_SELF_NODE_COUNT complexity constant
Enhancement	► rs/embedders/tests/system_api.rs     Update supported APIs to include SubnetSelfNodeCount
Enhancement	► rs/embedders/tests/wasmtime_embedder.rs     Import ic0.subnet_self_node_count in Wasmtime tests
Enhancement	► rs/execution_environment/src/query_handler/query_cache/tests.rs     Include SystemApiCallId::SubnetSelfNodeCount in expected list
Enhancement	► rs/execution_environment/tests/hypervisor.rs     Add subnet_self_node_count test scaffolding and WAT example
Enhancement	► rs/interfaces/src/execution_environment.rs     Extend SystemApiCallId enum with SubnetSelfNodeCount and declare ic0_subnet_self_node_count in SystemApi trait
Enhancement	► rs/test_utilities/execution_environment/src/lib.rs     Add with_subnet_size builder to configure subnet size in tests