feat: add MQTT QoS support and timestamp to A01 protocol payload

[NOisi-x]

Summary

Add MQTT QoS support pipeline and a Unix timestamp field to the A01 protocol — the two minimal, backward-compatible prerequisites needed for Zeo washer START commands to work over MQTT.

Motivation

The device firmware requires three conditions for a START command to be accepted:

1. QoS 1 — DP200 must be published at AT_LEAST_ONCE; the default AT_MOST_ONCE (QoS 0) is silently rejected by the broker.
2. Timestamp — A01 command payloads must include a "t" field with a Unix timestamp.
3. Parameter bundle — MODE, PROGRAM, and other wash parameters must be sent together with START in a single MQTT message.

This PR addresses (1) and (2) — the protocol-level infrastructure. (3) will follow in a separate PR built on top of this one.

These findings build upon the excellent reverse engineering work done in ndwzy/roborock_washer_ha — many thanks for the foundational research.

Changes

New MqttQos enum (roborock/mqtt/session.py)

class MqttQos(IntEnum):
    AT_MOST_ONCE = 0   # Fire-and-forget. No acknowledgment required.
    AT_LEAST_ONCE = 1  # Guaranteed delivery with possible duplicates. Broker sends PUBACK.
    EXACTLY_ONCE = 2   # Guaranteed delivery with no duplicates.

Thread qos through the publish chain

File	Change
roborock/mqtt/session.py	Abstract MqttSession.publish() gains qos parameter
roborock/mqtt/roborock_session.py	RoborockMqttSession.publish() & LazyMqttSession.publish() pass qos through
roborock/devices/transport/mqtt_channel.py	MqttChannel.publish() passes qos through
roborock/devices/rpc/a01_channel.py	send_decoded_command() gains qos parameter, passes it on non-query publishes
roborock/testing/channel.py	FakeChannel._publish() accepts qos for compatibility (not simulated)

Add timestamp to A01 payload (roborock/protocols/a01_protocol.py)

encode_mqtt_payload() now includes "t": int(time.time()) in every payload.

Tests & fixtures

• tests/devices/traits/a01/test_init.py — 4 assertions updated to tolerate "t" field
• tests/e2e/__snapshots__/test_device_manager.ambr — snapshot regenerated
• tests/fixtures/logging_fixtures.py — deterministic_message_fixtures now patches time.time for A01

Breaking changes

None. Every new qos parameter defaults to MqttQos.AT_MOST_ONCE (= 0), which is identical to the current hardcoded behavior. All existing callers work unchanged.

Reviewer notes

Addresses the following feedback from #871:

• [allenporter] Use an enum for QoS instead of raw integers
• [allenporter] Place docstrings below each enum value
• [allenporter] Move time.time monkeypatch into deterministic_message_fixtures

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Part of: #871 (closed)