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.

tests/integration/test_scenario_lifecycle.py

@@ -78,10 +78,8 @@ class TestScenarioLifecycle:
             json={"currency": "ca"},
         )
         assert invalid_update.status_code == 422
-        assert (
-            invalid_update.json()["detail"][0]["msg"]
-            == "Value error, Currency code must be a 3-letter ISO value"
-        )
+        assert "Invalid currency code" in invalid_update.json()[
+            "detail"][0]["msg"]
 
         # Scenario detail should still show the previous (valid) currency
         scenario_detail = client.get(f"/scenarios/{scenario_id}/view")