feat(generator): emit From{Unit} factory for every availableUnit (closes #48, replaces #67)

[matt-edmondson]

Summary

Closes #48. Replaces #67 (closed; the local sandbox proxy refused force-pushes to the original branch after rebasing onto current vectors, so the resolved commit lives here).

Previously QuantitiesGenerator emitted only From{firstUnit} on each generated type — Length had FromMeter but no FromKilometer/FromFoot/FromInch/FromMile, Mass had FromKilogram but no FromGram/FromPound, etc. Consumers had to convert manually before constructing a quantity.

This PR makes the generator emit a From{Unit} factory for every entry in a dimension's availableUnits, applying the conversion declared in units.json:

public static Length<T> FromMeter(T value)      => Create(value);
public static Length<T> FromKilometer(T value)  =>
    Create((value * T.CreateChecked(MetricMagnitudes.Kilo)));
public static Length<T> FromFoot(T value)       =>
    Create((value * T.CreateChecked(Units.ConversionConstants.FeetToMeters)));

The conversion expression honours:

• magnitude (Kilo, Centi, Nano, …) → MetricMagnitudes constants
• conversionFactor (FeetToMeters, PoundToKilograms, …) → ConversionConstants
• offset (CelsiusToKelvinOffset, FahrenheitToKelvinOffset) → additive after scaling

Implementation

• GeneratorBase.Initialize is now virtual so QuantitiesGenerator can override it to load both dimensions.json and units.json.
• New AddUnitFactories helper centralises emission so V0 base, V1 base, and overload paths produce identical factory shapes.
• New BuildToBaseExpression composes the conversion expression from the unit's metadata.
• The legacy abstract Generate is preserved as a shim for any other consumer of the generator.
• Coexists cleanly with the SEM001 diagnostic from feat(generator): emit SEM001 diagnostic for unknown dimension references #65 (both helper sets retained).

Test plan

Semantics.Test/Quantities/MultiUnitFactoryTests.cs covers identity for SI base units, magnitude scaling, conversion-factor scaling, time conversions, overload inheritance (Distance.FromKilometer, Diameter.FromMillimeter, Wavelength.FromNanometer), and storage-type genericity (float, decimal).

⚠️ Note about committed Generated/ files

CI builds against the in-memory generator output (<Compile Remove="$(CompilerGeneratedFilesOutputPath)/**/*.cs" />), so the new tests will run against the new emitted code. The on-disk Semantics.Quantities/Generated/*.g.cs files are not refreshed in this commit (no dotnet available locally). They'll regenerate on the next dotnet build.

🤖 Generated by Claude Code

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Generated by Claude Code

[sonarqubecloud]

Quality Gate failed

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

See analysis details on SonarQube Cloud

[matt-edmondson]

Superseded by #71.

This PR is dirty against current vectors because it was merged onto a vectors SHA from before #68 (V0 non-negativity / V0–V0 absolute subtraction) landed. I rebased it onto current vectors and resolved the conflict, but the sandbox proxy refused the force-push to work/issue-48-rebase (same 403 noted in this PR's own body re: #67 → #69). The resolved commit lives on claude/rebase-issue-48 and is up as #71.

Recommend closing this PR in favour of #71. Resolution summary on #71.

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Generated by Claude Code