[W7] Introduce Pydantic boundaries and supported static typing

[Claudio9701]

Outcome

Untrusted inputs and stable results have safe contracts without wrapping large native geospatial objects.

Parent tasks

• define runtime/static typing ADR and model conventions
• add coordinate, bounds, profile, region, OSRM config/status/result models
• separate public domain from private transport models
• add schema snapshots, exception translation, py.typed decision, and compatibility adapters
• migrate routing/download/geometry boundaries incrementally

Acceptance

CRS, coordinate order, units, nulls, and validation failures are explicit and tested.

Plan: PR #61