feat: Add Processing Opex functionality

- Introduced OpexValidationError for handling validation errors in processing opex calculations.
- Implemented ProjectProcessingOpexRepository and ScenarioProcessingOpexRepository for managing project and scenario-level processing opex snapshots.
- Enhanced UnitOfWork to include repositories for processing opex.
- Updated sidebar navigation and scenario detail templates to include links to the new Processing Opex Planner.
- Created a new template for the Processing Opex Planner with form handling for input components and parameters.
- Developed integration tests for processing opex calculations, covering HTML and JSON flows, including validation for currency mismatches and unsupported frequencies.
- Added unit tests for the calculation logic, ensuring correct handling of various scenarios and edge cases.

models/scenario.py

@@ -21,6 +21,7 @@ from services.currency import normalise_currency
 from .enums import ResourceType, ScenarioStatus, sql_enum
 from .profitability_snapshot import ScenarioProfitability
 from .capex_snapshot import ScenarioCapexSnapshot
+from .processing_opex_snapshot import ScenarioProcessingOpexSnapshot
 
 if TYPE_CHECKING:  # pragma: no cover
     from .financial_input import FinancialInput
@@ -91,6 +92,13 @@ class Scenario(Base):
         order_by=lambda: ScenarioCapexSnapshot.calculated_at.desc(),
         passive_deletes=True,
     )
+    processing_opex_snapshots: Mapped[List["ScenarioProcessingOpexSnapshot"]] = relationship(
+        "ScenarioProcessingOpexSnapshot",
+        back_populates="scenario",
+        cascade="all, delete-orphan",
+        order_by=lambda: ScenarioProcessingOpexSnapshot.calculated_at.desc(),
+        passive_deletes=True,
+    )
 
     @validates("currency")
     def _normalise_currency(self, key: str, value: str | None) -> str | None:
@@ -115,3 +123,11 @@ class Scenario(Base):
         if not self.capex_snapshots:
             return None
         return self.capex_snapshots[0]
+
+    @property
+    def latest_processing_opex(self) -> "ScenarioProcessingOpexSnapshot | None":
+        """Return the most recent processing opex snapshot for this scenario."""
+
+        if not self.processing_opex_snapshots:
+            return None
+        return self.processing_opex_snapshots[0]