feat(quantities): IPhysicalQuantity surface + typed In() (closes #59)

[matt-edmondson]

Summary

This PR contains the actual #59 implementation plus a small cleanup. The earlier PR #79 merged with only the docs commit; the implementation work was pushed to the same branch after merge and never went through CI on its own.

Closes #59 — canonical IPhysicalQuantity surface + typed In()

Implement the IPhysicalQuantity<T> contract decided in #59 with compile-time dimension safety on unit conversion.

Runtime:

• IPhysicalQuantity<T> now exposes Dimension (DimensionInfo), IComparable<IPhysicalQuantity<T>>, IEquatable<IPhysicalQuantity<T>>. CompareTo throws on cross-dimension comparison; Equals returns false (equality is total).
• IUnit gains Name/Symbol/Dimension/ToBaseFactor/ToBaseOffset plus default-implemented ToBase<T> / FromBase<T> over the affine conversion base = value × factor + offset.
• New UnitConversionException type (reserved for any future untyped path).

Generator:

• DimensionsGenerator emits a marker interface per dimension (I{Dim}Unit : IUnit).
• UnitsGenerator combines units.json with dimensions.json so each unit implements the right I{Dim}Unit marker(s). Emits class records with the full property surface, folds metric magnitude + conversionFactor into a single ToBaseFactor, and emits a static Units catalogue of singletons.
• QuantitiesGenerator emits Dimension override + typed In(I{Dim}Unit) on every V0/V1 base + V0/V1 overload type.

length.In(Units.Kilometer);   // ✓
length.In(Units.Kilogram);    // ❌ compile error — IMassUnit, not ILengthUnit

Cleanup commit

CI flagged 9 IDE0370 "Suppression is unnecessary" findings on the ! null-forgiving operator on return expressions in SemanticQuantity.cs and a reflection call site in SemanticString.cs. Create<TResult>() is non-nullable, so the suppression was noise. Also adds if-no-files-found: ignore to the Upload Coverage Report step so runs that don't produce coverage don't surface a workflow warning.

Out of scope (follow-up)

• V2/V3/V4 per-component In() (vector types don't implement IPhysicalQuantity).
• Fahrenheit-style scaled-plus-offset conversions (existing offset metadata is incorrect for these).

Heads-up — landed without local build verification

The sandbox build is blocked by an analyzer mismatch unrelated to this change (existing committed files fail IDE0055 on net8 with the current SDK). Generator changes shipped blind. CI is the source of truth on this one.

Test plan

• CI compiles Semantics.Quantities for all four TFMs (net7/8/9/10).
• CI runs PhysicalQuantityCoreTests (Length+Kilometer = 0.01, Temperature+Celsius = 26.85, CompareTo / Equals cross-dim behaviour).
• Removing the ! suppressions doesn't introduce CS86xx nullable warnings.
• Diff the regenerated Semantics.Quantities/Generated/ and verify the new Dimension + In(...) members appear on every V0/V1 type.

https://claude.ai/code/session_01LqtywMUn5GwFATD5FDdLn6

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Generated by Claude Code

[sonarqubecloud]

Quality Gate failed

Failed conditions
0.0% Coverage on New Code (required ≥ 80%)

See analysis details on SonarQube Cloud