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/test_currency.py

@@ -0,0 +1,42 @@
+from __future__ import annotations
+
+import pytest
+
+from services.currency import CurrencyValidationError, normalise_currency, require_currency
+
+
+@pytest.mark.parametrize(
+    "raw,expected",
+    [
+        ("usd", "USD"),
+        (" Eur ", "EUR"),
+        ("JPY", "JPY"),
+        (None, None),
+    ],
+)
+def test_normalise_currency_valid_inputs(raw: str | None, expected: str | None) -> None:
+    assert normalise_currency(raw) == expected
+
+
+@pytest.mark.parametrize("raw", ["usd1", "us", "", "12", "X Y Z"])
+def test_normalise_currency_invalid_inputs(raw: str) -> None:
+    with pytest.raises(CurrencyValidationError):
+        normalise_currency(raw)
+
+
+def test_require_currency_with_value() -> None:
+    assert require_currency("gbp", default="usd") == "GBP"
+
+
+def test_require_currency_with_default() -> None:
+    assert require_currency(None, default="cad") == "CAD"
+
+
+def test_require_currency_missing_default() -> None:
+    with pytest.raises(CurrencyValidationError):
+        require_currency(None)
+
+
+def test_require_currency_invalid_default() -> None:
+    with pytest.raises(CurrencyValidationError):
+        require_currency(None, default="invalid")