HEMS: add per-hems tests for nil statements when unconfigured or not connected

[andig]

Adds unit tests per HEMS asserting that Curtailed()/Dimmed() and the underlying power functions (CurtailedPercent, MaxConsumptionPower, MaxProductionPower) return nil when curtailment or dimming are not configured (FNN, Relay) or when no upstream controlbox has connected (EEBus).

• FNN: without W3 no curtailment statement, without W4 no dimming statement — passes
• Relay: never makes a curtailment statement, no dimming statement before the relay state is known — passes
• EEBus: TestNotConnected fails intentionally — MaxConsumptionPower, CurtailedPercent and hence Dimmed()/Curtailed() report values even though no controlbox ever connected. Only MaxProductionPower already returns nil. Tests expose the bug; no fix included per request.

Based on #31428.

🤖 Generated with Claude Code

[sourcery-ai]

Hey - I've left some high level feedback:

• In relay_test.go, assert.Equal(t, new(1e3), c.MaxConsumptionPower()) will not compile because new expects a type, not a value; consider using a small helper like ptr(1000.0) or taking the address of a typed literal instead.
• Since TestNotConnected in eebus_test.go is intentionally failing to highlight a bug, consider marking it with t.Skip and a clear TODO or gating it behind a build tag so that the main test suite can still pass until the underlying issue is fixed.
• The boolG helper in fnn_test.go is a useful pattern; if similar boolean getters are needed in other HEMS tests, consider consolidating it in a shared test utility to avoid duplication.

Prompt for AI Agents

Please address the comments from this code review:

## Overall Comments
- In `relay_test.go`, `assert.Equal(t, new(1e3), c.MaxConsumptionPower())` will not compile because `new` expects a type, not a value; consider using a small helper like `ptr(1000.0)` or taking the address of a typed literal instead.
- Since `TestNotConnected` in `eebus_test.go` is intentionally failing to highlight a bug, consider marking it with `t.Skip` and a clear TODO or gating it behind a build tag so that the main test suite can still pass until the underlying issue is fixed.
- The `boolG` helper in `fnn_test.go` is a useful pattern; if similar boolean getters are needed in other HEMS tests, consider consolidating it in a shared test utility to avoid duplication.

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[andig]

EEBus: TestNotConnected fails intentionally — MaxConsumptionPower, CurtailedPercent and hence Dimmed()/Curtailed() report values even though no controlbox ever connected. Only MaxProductionPower already returns nil. Tests expose the bug; no fix included per request.

@premultiply was würden wir hier erwarten? Genau dafür gibts ja egtl. die Failsafe Values?

[premultiply]

In dem Fall würde Passivität herrschen (dauerhaft nicht gedimmt) bzw. eine statische Vorgabe des Anlagenbetreibers wäre umzusetzen (z.B dauerhaft 100, 70, 60, 50 oder 0%. In anderen Ländern durchaus auch andere / freie Werte, häufig dann auch als Leistungswert mit dem Netzbetreiber vereinbart).

Fallback ist etwas anderes: Das gilt erst wenn diese Daten mindestens einmal von der Steuerbox auch tatsächlich übermittelt wurden und dann die Verbindung zu dieser bzw. zum Netzbetreiber temporär abbricht.