Cherry-pick Prometheus per-query metrics to release

[justinfrevert]

…22100] (#904)

• feat: add Prometheus per-query metrics to midnight data sources

Introduce MidnightDataSourceMetrics with public accessor methods, replacing the upstream McFollowerMetrics whose accessors are crate-private in partner-chains v1.8.1. The local observed_async_trait! macro now records call counts and timing histograms for all six midnight-specific data source methods (candidates, cnight observation, federated authority observation).

JIRA: PM-22100
Made-with: Cursor

• ci: normalise scan job name (ci: normalise scan job name #823)

• update scanner action to latest version

• update scanner action to latest version

• ci: rename workflow name from build to scan

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• chore: add change file for PM-22100 dbsync query metrics

Made-with: Cursor

• feat: add sub-query SQL-level Prometheus timing for midnight data sources

Add individual Prometheus timing histograms for each SQL query inside midnight-node data source methods. This provides per-query latency visibility alongside the existing method-level timing, enabling precise identification of slow DBSync queries on mainnet.

13 sub-query timers added across 3 data sources:

• cNight observation: 5 queries (block lookup + 4 concurrent UTXO queries)
• Federated authority: 3 queries (block lookup + 2 governance UTXOs)
• Candidates: 5 queries across 3 methods

Ref: PM-22100
Made-with: Cursor

• refactor: extract sub-query timer helper to reduce repetition

Replace 13 inline timer patterns with a shared start_sub_query_timer() helper and SubQueryTimer RAII guard in the metrics module. Each call site reduces from 3 lines to 1.

Made-with: Cursor

• refactor: remove method-level timing, keep SQL-level sub-query timers only

Remove the observed_async_trait! macro timing (method-level) since per-SQL-query timing provides more useful granularity. Simplify MidnightDataSourceMetrics to histogram-only (remove unused call counter). Rename metric to midnight_data_source_query_time_elapsed with query_name label for clarity.

Made-with: Cursor

• style: apply rustfmt to candidates data source

Made-with: Cursor

• chore: update changes file to reflect SQL-level sub-query timing

Made-with: Cursor

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Overview

🗹 TODO before merging

• Ready

📌 Submission Checklist

• Changes are backward-compatible (or flagged if breaking)
• Pull request description explains why the change is needed
• Self-reviewed the diff
• I have included a change file, or skipped for this reason:
• If the changes introduce a new feature, I have bumped the node minor version
• Update documentation (if relevant)
• Updated AGENTS.md if build commands, architecture, or workflows changed
• No new todos introduced

🧪 Testing Evidence

Please describe any additional testing aside from CI:

• Additional tests are provided (if possible)

🔱 Fork Strategy

• Node Runtime Update
• Node Client Update
• Other:
• N/A

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