Add Energy (measurement)

[vhrcgcom]

Description

Implement Energy as a ValueObject in the measurement module.

Spec: non-negative f64 with unit (J, kWh, cal)

Implementation checklist

• Create src/measurement/energy.rs
• Implement ValueObject trait
• Add #[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
• Export from src/measurement/mod.rs and prelude
• Unit tests: valid input · empty input · invalid format · normalisation
• Doc comment with # Example block
• Update status in ROADMAP.md from ⬜ to ✅

Implementation detail

Input / Output

Energy is a composite value object that carries both a numeric value and a unit.

	Type
Input	EnergyInput { value: f64, unit: EnergyUnit }
Output	String — e.g. "3600.0 J", "1.0 kWh"

Define a unit enum in the same file:

EnergyUnit { J, Kwh, Cal }

EnergyUnit must derive Debug, Clone, Copy, PartialEq.

Validation

• value must be >= 0.0 and finite.

Extra methods

• amount() -> f64
• unit() -> EnergyUnit
• to_joules() -> f64 — convert to joules at call time.

References

• ROADMAP.md
• CONTRIBUTING.md