feat: add overdue periods gauge

[silent-cipher]

Summary

Adds a new Prometheus gauge metric pdp_provider_overdue_periods that tracks estimated unrecorded overdue proving periods per provider in real-time. This gauge complements the existing cumulative counters by providing immediate visibility into providers that are behind on submitting proofs, even before the subgraph confirms the faults.

Changes

New Metric

• pdp_provider_overdue_periods (Gauge): Estimates overdue proving periods by calculating (currentBlock - (nextDeadline + 1) / maxProvingPeriod for each proof set where the deadline has passed
• Naturally resets to 0 when providers submit proofs and the subgraph catches up
• Independent of cumulative counter baselines, emitted on every poll

Subgraph Query Enhancement

• Extended GET_PROVIDERS_WITH_DATASETS query to fetch proofSets with overdue deadlines
• Added blockNumber parameter to filter proof sets where nextDeadline < currentBlock
• Fetches nextDeadline, and maxProvingPeriod per proof set

closes #374

[Copilot]

Pull request overview

Adds a real-time Prometheus gauge to complement existing PDP data-retention counters by estimating overdue proving periods per provider from subgraph deadlines.

Changes:

• Introduces pdp_provider_overdue_periods gauge and emits it on every data-retention poll.
• Extends PDP subgraph providers query to include overdue proofSets filtered by blockNumber.
• Updates validation/types and adds/extends unit tests for the new query fields and gauge behavior.

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
docs/checks/events-and-metrics.md	Documents the new pdp_provider_overdue_periods metric.
docs/checks/data-retention.md	Describes overdue estimation logic and how the new gauge differs from counters.
apps/backend/src/pdp-subgraph/types.ts	Adds blockNumber option and proofSets typing/validation.
apps/backend/src/pdp-subgraph/types.spec.ts	Extends validation tests for proofSets.
apps/backend/src/pdp-subgraph/queries.ts	Adds blockNumber variable and proofSets selection/filtering.
apps/backend/src/pdp-subgraph/pdp-subgraph.service.ts	Threads blockNumber through provider fetch requests and retries.
apps/backend/src/pdp-subgraph/pdp-subgraph.service.spec.ts	Updates service tests for the new query variable and response shape.
apps/backend/src/metrics-prometheus/metrics-prometheus.module.ts	Registers the new gauge metric provider.
apps/backend/src/data-retention/data-retention.service.ts	Computes overdue estimate and emits gauge; adds safe BigInt gauge setter.
apps/backend/src/data-retention/data-retention.service.spec.ts	Adds tests for gauge emission, cleanup removal, and large-value handling.

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[SgtPooki]

very quick look before vacation, but mostly lgtm.. @juliangruber can you take a peek as well?

[juliangruber]

would be nice to keep the warning if (for whatever reason, maybe, proving periods change, fast finality, etc) for some reason the value should overflow