Viessmann: add heat pump power, temperature and target readings

[ickeundso]

The Viessmann heat pump template only wired heating.dhw.oneTimeCharge. With no power reading, the loadpoint falls back to the current×phases×230V estimate and shows a wildly wrong charge power (up to ~11 kW while the compressor actually draws ~1.3 kW).

Charger template additions:

• power: heating.power.consumption.current — real electrical input power (kW → W)
• temp: heating.dhw.sensors.temperature.dhwCylinder — domestic hot water temperature on the loadpoint gauge
• limittemp: heating.dhw.temperature.main — the device's DHW target

All readers use the single device feature-list endpoint with a shared 120s cache: the Viessmann API has a strict daily request quota (shared with the ViCare app), and per-feature polling exhausts it within hours (HTTP 429). Since the http plugin caches by URL, identical-URL readers share one request per cache window (~720/day). Deliberately no energy reading: the API exposes no monotonic lifetime counter, and with power present evcc integrates energy itself.

Also adds a meter template (usage: aux) reading the same consumption value, for showing the heat pump in the energy flow when it is not configured as a charger.

Verified against a live Vitocal 250-A. make docs and template tests pass.

[sourcery-ai]

Hey - I've left some high level feedback:

• The same Viessmann features URI plus auth block is duplicated multiple times across charger and meter templates; consider extracting this into a shared anchor/include to keep configuration DRY and easier to adjust if the endpoint or auth parameters ever change.
• The meter template exposes a usage parameter but only allows the fixed value aux; if no other usage types are expected, you might simplify by inlining usage: aux to avoid an unnecessary configuration option in the UI.

Prompt for AI Agents

Please address the comments from this code review:

## Overall Comments
- The same Viessmann features URI plus auth block is duplicated multiple times across charger and meter templates; consider extracting this into a shared anchor/include to keep configuration DRY and easier to adjust if the endpoint or auth parameters ever change.
- The meter template exposes a `usage` parameter but only allows the fixed value `aux`; if no other usage types are expected, you might simplify by inlining `usage: aux` to avoid an unnecessary configuration option in the UI.

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