Meter (Growatt TL-XH): write battery-first time slot atomically

[andig]

fixes #23300

The battery-mode switch wrote the "battery first" Time-1 slot as two separate single-register FC16 writes (start time 3038, then end time 3039). The TL-XH/MOD-XH firmware ACKs 3038 but rejects the standalone write to 3039 with modbus exception 0, so the sequence aborts before reaching 3049 and the requested hold never engages (battery keeps discharging into the car). The per-cycle retry also spams battery mode: modbus: exception '0', function '16'.

Per the Growatt protocol, 3038/3039 form one time-period pair and must be set together via write multiple, the same atomicity the existing MIX/SPH growatt-hybrid template documents.

• write start+end as a single FC16 transaction: one uint32 write to 3038 (0xA000173B = (40960 << 16) | 5947), which evcc encodes big-endian as [3038]=0xA000, [3039]=0x173B
• AcChargeEnable (3049) still written separately

TODO

• hardware validation: the fix is derived from the trace in the issue and the vendor protocol but not yet confirmed on-device. Waiting for the reporter to verify hold works without the exception.

[sourcery-ai]

Hey - I've found 1 issue, and left some high level feedback:

• The large uint32 constants (536876859, 2684360507) are hard to read and verify; consider expressing them as computed values (e.g. (8192 << 16) | 5947 / 0x2000173B) or via named variables to make the intent and calculation clearer.
• The sequences for the enabled time slot are duplicated with the same constant and Modbus write in multiple branches; consider factoring this into a shared helper or template block to avoid divergence if the register layout changes again.

Prompt for AI Agents

Please address the comments from this code review:

## Overall Comments
- The large uint32 constants (536876859, 2684360507) are hard to read and verify; consider expressing them as computed values (e.g. `(8192 << 16) | 5947` / `0x2000173B`) or via named variables to make the intent and calculation clearer.
- The sequences for the enabled time slot are duplicated with the same constant and Modbus write in multiple branches; consider factoring this into a shared helper or template block to avoid divergence if the register layout changes again.

## Individual Comments

### Comment 1
<location path="templates/definition/meter/growatt-hybrid-tlxh.yaml" line_range="153" />
<code_context>
       set:
         source: sequence
         set:
+        # value = (start << 16) | end = (40960 << 16) | 5947 = 0xA000173B; bit15=1 -> slot enabled
         - source: const
-          value: 40960
</code_context>
<issue_to_address>
**suggestion:** Clarify which word and bit the `bit15` reference applies to in the packed value.

The packed value is `(start << 16) | end`, so it’s unclear whether `bit15` refers to the `start` or `end` 16-bit word. Please update the comment to explicitly state which 16‑bit word’s bit 15 controls the slot enable (e.g., `bit15 of the start word`).

```suggestion
        # value = (start << 16) | end = (40960 << 16) | 5947 = 0xA000173B; bit15 of the start word (high 16 bits) = 1 -> slot enabled
```
</issue_to_address>

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[sourcery-ai]

suggestion: Clarify which word and bit the bit15 reference applies to in the packed value.

The packed value is (start << 16) | end, so it’s unclear whether bit15 refers to the start or end 16-bit word. Please update the comment to explicitly state which 16‑bit word’s bit 15 controls the slot enable (e.g., bit15 of the start word).

Suggested change

	# value = (start << 16) | end = (40960 << 16) | 5947 = 0xA000173B; bit15=1 -> slot enabled
	# value = (start << 16) | end = (40960 << 16) | 5947 = 0xA000173B; bit15 of the start word (high 16 bits) = 1 -> slot enabled