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_pricing.py

@@ -0,0 +1,155 @@
+from __future__ import annotations
+
+import math
+
+import pytest
+
+from services.pricing import (
+    PricingInput,
+    PricingMetadata,
+    PricingResult,
+    calculate_pricing,
+)
+
+
+def test_calculate_pricing_with_explicit_penalties() -> None:
+    pricing_input = PricingInput(
+        metal="copper",
+        ore_tonnage=100_000,
+        head_grade_pct=1.2,
+        recovery_pct=90,
+        payable_pct=96,
+        reference_price=8_500,
+        treatment_charge=100_000,
+        smelting_charge=0,
+        moisture_pct=10,
+        moisture_threshold_pct=8,
+        moisture_penalty_per_pct=3_000,
+        impurity_ppm={"As": 100},
+        impurity_thresholds={"As": 0},
+        impurity_penalty_per_ppm={"As": 2},
+        premiums=50_000,
+        fx_rate=1.0,
+        currency_code="usd",
+    )
+
+    result = calculate_pricing(pricing_input)
+
+    assert isinstance(result, PricingResult)
+    assert math.isclose(result.payable_metal_tonnes, 1_036.8, rel_tol=1e-6)
+    assert math.isclose(result.gross_revenue, 1_036.8 * 8_500, rel_tol=1e-6)
+    assert math.isclose(result.moisture_penalty, 6_000, rel_tol=1e-6)
+    assert math.isclose(result.impurity_penalty, 200, rel_tol=1e-6)
+    assert math.isclose(result.net_revenue, 8_756_600, rel_tol=1e-6)
+    assert result.treatment_smelt_charges == pytest.approx(100_000)
+    assert result.currency == "USD"
+
+
+def test_calculate_pricing_with_metadata_defaults() -> None:
+    metadata = PricingMetadata(
+        default_payable_pct=95,
+        default_currency="EUR",
+        moisture_threshold_pct=7,
+        moisture_penalty_per_pct=2_000,
+        impurity_thresholds={"Pb": 50},
+        impurity_penalty_per_ppm={"Pb": 1.5},
+    )
+
+    pricing_input = PricingInput(
+        metal="lead",
+        ore_tonnage=50_000,
+        head_grade_pct=5,
+        recovery_pct=85,
+        payable_pct=None,
+        reference_price=2_000,
+        treatment_charge=30_000,
+        smelting_charge=20_000,
+        moisture_pct=9,
+        moisture_threshold_pct=None,
+        moisture_penalty_per_pct=None,
+        impurity_ppm={"Pb": 120},
+        premiums=12_000,
+        fx_rate=1.2,
+        currency_code=None,
+    )
+
+    result = calculate_pricing(pricing_input, metadata=metadata)
+
+    expected_payable = 50_000 * 0.05 * 0.85 * 0.95
+    assert math.isclose(result.payable_metal_tonnes,
+                        expected_payable, rel_tol=1e-6)
+    assert result.moisture_penalty == pytest.approx((9 - 7) * 2_000)
+    assert result.impurity_penalty == pytest.approx((120 - 50) * 1.5)
+    assert result.treatment_smelt_charges == pytest.approx(50_000)
+    assert result.currency == "EUR"
+    assert result.net_revenue > 0
+
+
+def test_calculate_pricing_currency_override() -> None:
+    pricing_input = PricingInput(
+        metal="gold",
+        ore_tonnage=10_000,
+        head_grade_pct=2.5,
+        recovery_pct=92,
+        payable_pct=98,
+        reference_price=60_000,
+        treatment_charge=40_000,
+        smelting_charge=10_000,
+        moisture_pct=5,
+        moisture_threshold_pct=7,
+        moisture_penalty_per_pct=1_000,
+        premiums=25_000,
+        fx_rate=1.0,
+        currency_code="cad",
+    )
+
+    metadata = PricingMetadata(default_currency="USD")
+
+    result = calculate_pricing(
+        pricing_input, metadata=metadata, currency="CAD")
+
+    assert result.currency == "CAD"
+    assert result.net_revenue > 0
+
+
+def test_calculate_pricing_multiple_inputs_aggregate() -> None:
+    metadata = PricingMetadata(default_currency="USD")
+    inputs = [
+        PricingInput(
+            metal="copper",
+            ore_tonnage=10_000,
+            head_grade_pct=1.5,
+            recovery_pct=88,
+            payable_pct=95,
+            reference_price=8_000,
+            treatment_charge=20_000,
+            smelting_charge=5_000,
+            moisture_pct=7,
+            moisture_threshold_pct=8,
+            moisture_penalty_per_pct=1_000,
+            premiums=0,
+            fx_rate=1.0,
+            currency_code=None,
+        ),
+        PricingInput(
+            metal="copper",
+            ore_tonnage=8_000,
+            head_grade_pct=1.1,
+            recovery_pct=90,
+            payable_pct=96,
+            reference_price=8_000,
+            treatment_charge=18_000,
+            smelting_charge=4_000,
+            moisture_pct=9,
+            moisture_threshold_pct=8,
+            moisture_penalty_per_pct=1_000,
+            premiums=0,
+            fx_rate=1.0,
+            currency_code="usd",
+        ),
+    ]
+
+    results = [calculate_pricing(i, metadata=metadata) for i in inputs]
+
+    assert all(result.currency == "USD" for result in results)
+    assert sum(result.net_revenue for result in results) > 0