feat: Export million_round_instructions_total in subnet_metrics

[schneiderstefan]

This commit adds an addition field returned with the subnet_metrics management canister endpoint. It tracks the existing prometheus metric execution_round_instructions, except that it does not get reset on replica start.

One user of the existing metric and the new value are the public dashboards, with the off-chain dashboard currently relying on the prometheus metric.

The new value starts at 0 with the introduction of this commit. Like the metric, the new field counts the executed wasm instructions, plus instruction overheads the scheduler uses (e.g. there is a base overhead per message).

While the instructions are tracked exactly internally, they are only exported in millions of instructions.

As a drive-by, this commit also fixes an issue where the metric/new total was not correctly tracked in the edge case of heap delta rate limiting kicking in.

[schneiderstefan]

Intended follow-up once this is rolled out: #11586

[zeropath-ai]

✅ No security or compliance issues detected. Reviewed everything up to c6df79f.

Security Overview

• 🔎 Scanned files: 17 changed file(s)
• 🔗 Scan Link: https://zeropath.com/app/repositories/f5e9d2bb-29a4-4b64-902a-391d65fd8b2d?scanId=c0da9ee4-fa51-488f-a33c-728e29769550&codeScanTypes=PrScan&tab=issues

Detected Code Changes

Change Type	Relevant files
Enhancement	► rs/execution_environment/src/execution_environment.rs     Reporting new million_round_instructions_total in subnet metrics computation and mapping from metrics.round_instructions_total (div_ceil)
Enhancement	► rs/execution_environment/src/metrics.rs     Add instructions() accessor to MeasurementScope
Enhancement	► rs/execution_environment/src/scheduler.rs     Introduce accumulate_round_subnet_metrics to aggregate round metrics; update round_subnet metrics accumulation on exits
Enhancement	► rs/execution_environment/src/scheduler/tests/rate_limiting.rs     Add test ensuring drained consensus queue messages are counted toward update_transactions_total and that round instructions are tracked across rounds
Enhancement	► rs/execution_environment/tests/execution_test.rs     Update subnet metrics test to account for round_instructions_total and its relation to million rounding behavior
Enhancement	► rs/protobuf/def/state/metadata/v1/metadata.proto     Add round_instructions_total field to SubnetMetrics (tag 13)
Enhancement	► rs/protobuf/src/gen/state/state.metadata.v1.rs     Include optional round_instructions_total field in SubnetMetrics struct
Enhancement	► rs/replicated_state/src/metadata_state.rs     Add round_instructions_total field to SubnetMetrics
Enhancement	► rs/replicated_state/src/metadata_state/proto.rs     Serialize/deserialize round_instructions_total in SubnetMetrics
Enhancement	► rs/replicated_state/src/metadata_state/tests.rs     Test decoding of zero when round_instructions_total field absent
Enhancement	► rs/state_manager/src/manifest/split/tests.rs     Update expected size/hash for SYSTEM_METADATA_FILE and related entries due to new round_instructions_total field
Enhancement	► rs/state_manager/tests/state_manager.rs     New test: round_instructions_total_survives_a_checkpoint
Enhancement	► rs/test_utilities/state/src/lib.rs     Propagate round_instructions_total in SubnetMetrics generation for tests
Enhancement	► rs/types/management_canister_types/src/lib.rs     Update SubnetMetricsArgs/docs to include million_round_instructions_total
Enhancement	► rs/types/management_canister_types/tests/ic.did     Update DID interface to document million_round_instructions_total field