MAINT Extract scenario-history page queries from MemoryInterface #2766

Is your feature request related to a problem? Please describe.

MemoryInterface.get_scenario_run_history_page() combines filter normalization, cursor pagination, SQL column selection, row conversion, and aggregate lookup inside the same large class that handles messages, scores, seeds, and other persistence operations. The history-page portion is a cohesive unit that can be understood separately without changing the public API.

This is M1, the first of three small scenario-history extraction steps. It is ready for implementation. Later steps cover attempt-to-work-unit matching and aggregate counters; do not include those extractions here.

Describe the solution you'd like

Extract the history-page query and row-to-record conversion into a private, typed component in the memory package. Keep MemoryInterface.get_scenario_run_history_page() as the public entry point, with its existing signature and return shape. It should delegate page retrieval and continue using the existing aggregate method for now.

• Move only page-specific filtering, validation, cursor handling, compact row selection, and record construction, including the directly related start-time parsing helper where appropriate.
• Reuse the existing backend-specific expressions through a narrow internal boundary. Do not copy SQL implementations or expose a new public API.
• Keep database access in memory. Do not move queries into the backend service or move scenario execution/presentation policy into memory.
• Wire the extracted implementation immediately. This is not a scaffolding-only change.

Acceptance criteria:

• Existing callers receive the same records, aggregate mapping, and has_more value.
• Scenario/registry-name, status, and label filters preserve current normalization and validation.
• Limits and invalid cursor IDs behave as before; timestamp ties use the existing ID tiebreaker with no skipped or duplicated rows across pages.
• The query still selects compact columns and uses limit + 1, without hydrating full result objects or introducing per-row queries.
• Empty pages and legacy/malformed start-time values preserve their current behavior.
• Existing SQLite and SQL Server expression hooks remain usable; focused memory and service coverage protects the delegation boundary.

Describe alternatives you've considered, if relevant

Moving the whole scenario-history subsystem at once makes a much larger review. Extracting every conditional into a separate helper adds navigation without clarifying ownership. Prefer one cohesive internal query module that the later matching and aggregation steps can extend, not a separate service per step.

Additional context

Starting points: pyrit/memory/memory_interface.py, get_scenario_run_history_page, _parse_scenario_started_at, and the scenario-history backend expression hooks. Consumers and coverage: pyrit/backend/services/scenario_run_service.py, tests/unit/memory/memory_interface/test_interface_scenario_history.py, and tests/unit/backend/test_scenario_run_service.py.

Follow doc/code/framework.md and the applicable database, Python, and test instructions. This is a behavior-preserving extraction, not a database migration, history API redesign, or counter-policy change. The separate observation-aware LLM scoring proposal is deferred and out of scope.

Series: #2766 (history pages), #2768 (attempt-to-work-unit matching), then #2769 (aggregate queries and records).