Write 32-bit modbus registers high-word-first on S series pumps

[Copilot]

Pull Request Type

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• Feature
• Bug Fix

Description

Heatpump model: S1256 (all S series)

Firmware version: N/A

S series pumps are asymmetric over modbus: 32-bit read responses come back low-word-first, but FC16 writes must be high-word-first. word_swap was applied to both directions, so no setting worked for both — with word_swap: true every 32-bit write was ACKed and silently discarded, with false every read decoded garbage.

Ground truth for 40012 "Degree minutes" (s32, factor 10) at 20.5 °C: the pump reads back [205, 0] and only accepts [0, 205] on write.

Changes

• CoilDataEncoderModbus: new optional word_swap_write overriding the word order used for encoding only. Unset (None) keeps word_swap for both directions, so nothing changes for existing callers.
• Modbus: passes word_swap_write=False when the pump model is Series.S, so 32-bit writes always go out high-word-first while reads keep honouring word_swap. F series (Modbus 40, which has the symmetric Modbus40 Word Swap register 48852) and pumps with no model set are unaffected.
• Tests: added coverage for the asymmetric encoder and for F series writes staying symmetric; updated the existing S1255-fixture 32-bit write expectations, which encoded the broken order.

hp = HeatPump(Model.S1256)
hp.word_swap = True
conn = Modbus(hp, "tcp://192.168.1.2:502", 1)

await conn.read_coil(coil)              # [205, 0] -> 20.5
await conn.write_coil(CoilData(coil, 20.5))  # -> [0, 205]

Checklist

• I have followed the instructions
• I ensured that my changes are well tested

• Fixes All writable 32-bit registers are written with reversed word order on S-series Modbus TCP #314