feat: Enhance currency handling and validation across scenarios

- Updated form template to prefill currency input with default value and added help text for clarity.
- Modified integration tests to assert more descriptive error messages for invalid currency codes.
- Introduced new tests for currency normalization and validation in various scenarios, including imports and exports.
- Added comprehensive tests for pricing calculations, ensuring defaults are respected and overrides function correctly.
- Implemented unit tests for pricing settings repository, ensuring CRUD operations and default settings are handled properly.
- Enhanced scenario pricing evaluation tests to validate currency handling and metadata defaults.
- Added simulation tests to ensure Monte Carlo runs are accurate and handle various distribution scenarios.

models/financial_input.py

@@ -31,6 +31,7 @@ from sqlalchemy.sql import func
 
 from config.database import Base
 from .metadata import CostBucket
+from services.currency import normalise_currency
 
 if TYPE_CHECKING:  # pragma: no cover
     from .scenario import Scenario
@@ -73,16 +74,12 @@ class FinancialInput(Base):
         DateTime(timezone=True), nullable=False, server_default=func.now(), onupdate=func.now()
     )
 
-    scenario: Mapped["Scenario"] = relationship("Scenario", back_populates="financial_inputs")
+    scenario: Mapped["Scenario"] = relationship(
+        "Scenario", back_populates="financial_inputs")
 
     @validates("currency")
     def _validate_currency(self, key: str, value: str | None) -> str | None:
-        if value is None:
-            return value
-        value = value.upper()
-        if len(value) != 3:
-            raise ValueError("Currency code must be a 3-letter ISO 4217 value")
-        return value
+        return normalise_currency(value)
 
     def __repr__(self) -> str:  # pragma: no cover
         return f"FinancialInput(id={self.id!r}, scenario_id={self.scenario_id!r}, name={self.name!r})"