Update tuya.ts

## Add support for Nova Digital ZIG-04 W/B and ZIG-06 W/B switches

This PR adds support for two Nova Digital wall switch models that were previously unsupported:

* Nova Digital ZIG-04 W/B (4-gang)
* Nova Digital ZIG-06 W/B (6-gang)

### Added fingerprints

#### 4-gang model

Added fingerprint:

```text
_TZE204_tayx2ud6
```

White label added:

```text
Nova Digital ZIG-04 W/B
```

#### 6-gang model

Added fingerprint:

```text
_TZE204_tpnnym5s
```

White label added:

```text
Nova Digital ZIG-06 W/B
```

---

## Device investigation

The implementation was based on information obtained directly from the Tuya IoT Platform device model definitions.

Although both devices belong to the same TS0601 switch family, their firmware exposes different datapoints and capabilities.

### ZIG-04 W/B (4-gang)

The Tuya device model exposes:

| DP   | Function                    |
| ---- | --------------------------- |
| 1-4  | switch_1 ... switch_4       |
| 7-10 | countdown_1 ... countdown_4 |
| 14   | relay_status                |
| 16   | backlight_switch            |
| 19   | switch_inching              |
| 209  | cycle_timing                |
| 210  | random_timing               |

Notably, this model does **not** expose a `light_mode` datapoint.

### ZIG-06 W/B (6-gang)

The Tuya device model exposes:

| DP   | Function                    |
| ---- | --------------------------- |
| 1-6  | switch_1 ... switch_6       |
| 7-12 | countdown_1 ... countdown_6 |
| 14   | relay_status                |
| 15   | light_mode                  |
| 16   | backlight_switch            |
| 19   | switch_inching              |
| 106  | child_lock                  |
| 209  | cycle_timing                |
| 210  | random_timing               |

---

## Added functionality

### 4-gang model

Added support for:

#### DP14 - relay_status

Mapped to:

```text
power_on_behavior
```

Values:

```text
off
on
memory
```

#### DP16 - backlight_switch

Mapped as a boolean entity:

```text
backlight_switch
```

---

### 6-gang model

The existing definition already supported:

#### DP14 - relay_status

Mapped to:

```text
power_on_behavior
```

#### DP15 - light_mode

Mapped to:

```text
indicator_mode
```

Values:

```text
none
relay
pos
```

This PR additionally adds support for:

#### DP16 - backlight_switch

Mapped as a boolean entity:

```text
backlight_switch
```

---

## Notes

During testing it was verified that:

* The 4-gang model does not implement `light_mode`.
* The 6-gang model implements both `light_mode` and `backlight_switch`.
* The two devices therefore cannot share exactly the same DP mapping despite belonging to the same TS0601 family.
* The mappings included in this PR match the Tuya cloud device definitions and were validated against the actual devices.

No existing fingerprints or datapoint mappings were modified; this PR only extends support for additional Nova Digital variants and exposes functionality already implemented by the device firmware.

Author: mrctorres