Add C# UnitTabulator code-generator and Rust unit_converter runtime

[Copilot]

Adds unit conversion support across the codegen pipeline and Rust facilities crate, backed by QUDT ontology data.

C# UnitTabulator (codegen2/src/Azure.Iot.Operations.UnitTabulator)

• CLI tool that reads QUDT RDF turtle files (qudt.unit.ttl, qudt.quantityKind.ttl) and emits two Rust source files via T4 templates:
  • ece_codes.rs — static HashMap from UNECE common codes → QUDT unit names
  • unit_infos.rs — static HashMap from QUDT unit names → UnitInfo (kind, multiplier, offset)
• Selects the canonical QuantityKind for each unit by picking the kind with the most applicable units (breaks ties toward units usable in real conversions)

Rust unit_converter (rust/azure_iot_operations_facilities/src/unit_converter)

• get_converter(source_unit, target_unit) -> Result<UnitConverter, ConvertError> resolves units by ECE code, unit: term, or full QUDT URI and validates kind compatibility
• UnitConverter { multiplier, offset } applies the affine transform val * multiplier + offset
• ConvertError variants: SourceUnitUnrecognized, TargetUnitUnrecognized, UnitsOfDifferentKinds, UnrepresentableValue
• Re-exported from crate root; integration tests in tests/unit_converter_tests.rs

let converter = get_converter("FAH", "unit:DEG_C")?;
let celsius = converter.convert(212.0)?; // 100.0

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