feat(sonoff): retain SWV irrigation plan slots by index

[MaxRink]

What

Adds per-slot retention for SONOFF SWV/SWV-ZFE irrigation plan reports:

• keeps the existing irrigation_plan_report as the last report received
• adds irrigation_plan_report_0 ... irrigation_plan_report_5 so reports are retained by plan_index instead of overwritten
• documents the limitation that the device protocol reports a single plan object at a time and no confirmed safe active per-slot read command is known yet

Why

The valve supports up to 6 irrigation plan slots, but the current converter exposes only the last pushed report. When the device reports another slot, Home Assistant loses the previous slot state. Retaining by plan_index lets HA show/read each slot independently once the device has pushed it.

Discovery / live test

Tested on live SONOFF SWV-ZFE Bewässerungsventil (0xa4c1381456c7ffff, firmware 1.0.7) in Zigbee2MQTT 2.12.1-dev.

Safe discovery steps:

• Existing irrigation_schedule_status GET reads attribute irrigationScheduleStatus and does not trigger plan reports.
• Existing plan report state before the change showed only the last pushed report (plan_index: 2).
• A conservative candidate command using custom cluster 0xfc11, command id 0x09, payload [0] was sent once and again after restart. Zigbee2MQTT logged the outgoing customClusterEwelink.readIrrigationPlan({data:[0]}), but the device did not return an irrigationPlanReport; therefore active on-demand read is not included in this PR.

Live deployed fallback build confirmed:

• Zigbee2MQTT starts healthy.
• HA discovery/state includes irrigation_plan_report_0 ... _5 alongside the legacy irrigation_plan_report.
• Slot entities are initially empty until the device pushes those specific slots, which is expected for retention-only behavior.

Screenshot: plan-slots-01-devtools-states.png captured from HA Developer Tools.

Validation

• corepack pnpm run check passes (Biome prints an existing schema-version info).
• corepack pnpm run build passes.
• corepack pnpm exec vitest run test/sonoff.test.ts has the new retention test passing; one unrelated existing SWV configure test fails in this sandbox because installed zigbee-herdsman@10.6.2 makes Device.save() access undefined internals.
• corepack pnpm test has the Sonoff tests including the new test passing; one unrelated batteryState.test.ts test times out at 5s in this sandbox.

cc @CubeZ2mDeveloper

Related: Koenkk/zigbee2mqtt#32545, #12647

[github-actions]

External review required

This PR modifies files that require review from their code owners before merging.

@CubeZ2mDeveloper:

• src/devices/sonoff.ts

Once reviewed, add the external-reviewer-approved label to unblock this check.

[MaxRink]

@CubeZ2mDeveloper — a question on the SWV/SWV-ZFE irrigation-plan protocol, if you can help:

This PR retains irrigationPlanReport (0x09) responses per plan_index so each configured slot is individually visible in Home Assistant. But it's currently passive — the per-slot entities only populate when the device pushes a report (e.g. on plan create/change). There doesn't appear to be a documented on-demand read command.

Is there a command to actively request an irrigation plan by index (so a controller can read slots 0–5 on demand and show all configured plans)? The custom customClusterEwelink cluster exposes commands readRecord, irrigationPlanSettings (0x06, write), irrigationPlanRemove, rainDelay, and the irrigationPlanReport (0x09) response. I tried issuing 0x09 with a plan_index payload but the device sent no report back.

Specifically:

1. Is there a read/query command ID (and payload format) that makes the device emit irrigationPlanReport for a given plan_index (or dump all slots)?
2. Does the device proactively report all configured plans at any point (interview / reconnect / after a schedule-status read), or only the last-changed plan?
3. If there's no read command, is retaining pushed reports per index (as here) the right approach, or would you prefer a different model?