refactor(BA-6630): move scheduler value types to the data layer to cut sokovan↔repositories cycles

[fregataa]

Summary

Removes the cross-layer import cycle between manager/sokovan and manager/repositories/scheduler by relocating shared value types (data) out of the logic layers into data/, and moving the logic that lived on those data types into its callers.

Three focused commits:

1. session-creation types → data/session/creation — ImageInfo, ContainerUserInfo, ScalingGroupNetworkInfo, DeploymentContext (+ its UserContext/ContainerUserContext/ImageContext/ResolvedPresetValues helpers). The sokovan scheduling-controller rule modules now depend on data/, not repositories/.
2. sokovan.data package → data.sokovan — so repositories/scheduler no longer imports the sokovan package for its value objects. To keep data/ free of upward imports, SessionAllocation.from_agent_selections (which referenced the selector-layer AgentSelection) was dropped and its logic moved into its only caller, SessionProvisioner._build_session_allocation.
3. remaining repositories/scheduler → sokovan back-edges — relocated AgentInfo and HandlerSessionData/HandlerKernelData into data/sokovan, and moved AgentInfo.from_meta_and_occupancy into its only caller, SessionProvisioner._build_agent_info.

Net result: repositories/scheduler → sokovan (logic) import edges = 0. Data flows downward only; the moved data types keep their plain-@dataclass style consistent with the existing data/sokovan package.

Principle applied throughout: data modules hold types only — no logic. Factory methods that referenced upper layers were moved to their (single) callers.

Out of scope (follow-up)

repositories/fair_share and repositories/resource_usage_history still import sokovan.scheduler.fair_share result types (4 TYPE_CHECKING edges) — same pattern, separate change.

Test plan

• pants fmt / fix / lint (incl. visibility) pass
• pants check (mypy, full) passes
• pants test (CI)

Resolves BA-6630