Add Power (measurement)

[vhrcgcom]

Description

Implement Power as a ValueObject in the measurement module.

Spec: non-negative f64 with unit (W, kW, hp)

Implementation checklist

• Create src/measurement/power.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

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

	Type
Input	PowerInput { value: f64, unit: PowerUnit }
Output	String — e.g. "1500.0 W", "1.5 kW"

Define a unit enum in the same file:

PowerUnit { W, Kw, Hp }

PowerUnit must derive Debug, Clone, Copy, PartialEq.

Validation

• value must be >= 0.0 and finite.

Extra methods

• amount() -> f64
• unit() -> PowerUnit
• to_watts() -> f64 — convert to watts at call time.

References

• ROADMAP.md
• CONTRIBUTING.md