Revert "Remove UART thread (#598)"

[puddly]

This reverts commit 1ac01ed.

The UART thread unfortunately is still necessary: even though writes are done outside of the event loop, notifications to read the serial port's file descriptor are not and any event loop slowdown will cause traffic from the radio to the library to effectively be halted.

Example:

2023-12-28 14:05:17.843 DEBUG (MainThread) [serialpy.descriptor_transport] Event loop woke up reader
2023-12-28 14:05:17.843 DEBUG (MainThread) [serialpy.descriptor_transport] Received b"\x07t\xb1\xedT.\x14\xb6R\x95K%\xabU\x920b\xe07t\x121o\x93=\xccf\x8c\xdd\xec;{\x1f~\x17t\xb1\xedT.\x14\xb6R\x95K%\xabU\x923`\xe37t\x121o\x93<\xcck\x8c\xdd]?\xc4}3~'t\xb1\xedT.\x14\xb6R\x95K%\xabU\x922k\xe17t\x121o\x93?\xcch\x8c\xd5w?\x8c\xe1~7t\xb1\xedT.\x14\xb0^\x95K%\xabU\x925c\xe37t\x121k\x93>\xccc\x89\xd9\xd2\x8b\xfe\xe6\xcd\xdex\x8f~Gt\xb1\xedT.\x14\xb6R\x95K%\xabU\x924{\xe37t\x121o\x939\xcck\x8c\xdd]?\xa2}8~\x0ft\xb1\xedT.\x14\xb6R\x95K%\xabU\x920b\xe07t\x121o\x93=\xccf\x8c\xdd\xec;J\xd3~\x1ft\xb1\xedT.\x14\xb6R\x95K%\xabU\x923`\xe37t\x121o\x93<\xcck\x8c\xdd]?\xf5\xdf~/t\xb1\xedT.\x14\xb6R\x95K%\xabU\x922k\xe17t\x121o\x93?\xcch\x8c\xd5w?\xbd-~?t\xb1\xedT.\x14\xb0^\x95K%\xabU\x925c\xe37t\x121k\x93>\xccc\x89\xd9\xd2\x8b\xfe\xe6\xcd\xdeqD~Ot\xb1\xedT.\x14\xb6R\x95K%\xabU\x924{\xe37t\x121o\x939\xcck\x8c\xdd]?\x93\xd4~\x0ft\xb1\xedT.\x14\xb6R\x95K%\xabU\x920b\xe07t\x121o\x93=\xccf\x8c\xdd\xec;J\xd3~\x1ft\xb1\xedT.\x14\xb6R\x95K%\xabU\x923`\xe37t\x121o\x93<\xcck\x8c\xdd]?\xf5\xdf~/t\xb1\xedT.\x14\xb6R\x95K%\xabU\x922k\xe17t\x121o\x93?\xcch\x8c\xd5w?\xbd-~?t\xb1\xedT.\x14\xb0^\x95K%\xabU\x925c\xe37t\x121k\x93>\xccc\x89\xd9\xd2\x8b\xfe\xe6\xcd\xdeqD~Ot\xb1\xedT.\x14\xb6R\x95K%\xabU\x924{\xe37t\x121o\x939\xcck\x8c\xdd]?\x93\xd4~\x0ft\xb1\xedT.\x14\xb6R\x95K%\xabU\x920b\xe07t\x121o\x93=\xccf\x8c\xdd\xec;J\xd3~\x1ft\xb1\xedT.\x14\xb6R\x95K%\xabU\x923`\xe37t\x121o\x93<\xcck\x8c\xdd]?\xf5\xdf~/t\xb1\xedT.\x14\xb6R\x95K%\xabU\x922k\xe17t\x121o\x93?\xcch\x8c\xd5w?\xbd-~?t\xb1\xedT.\x14\xb0^\x95K%\xabU\x925c\xe37t\x121k\x93>\xccc\x89\xd9\xd2\x8b\xfe\xe6\xcd\xdeqD~Ot\xb1\xedT.\x14\xb6R\x95K%\xabU\x924{\xe37t\x121o\x939\xcck\x8c\xdd]?\x93\xd4~\xc2\x02Q\xa8\xbd~"
2023-12-28 14:05:17.843 DEBUG (MainThread) [serialpy.descriptor_transport] Immediately writing b'\x81`Y~'
2023-12-28 14:05:17.844 DEBUG (MainThread) [serialpy.descriptor_transport] Sent 4 of 4 bytes
2023-12-28 14:05:17.844 DEBUG (MainThread) [bellows.ezsp.protocol] Application frame received incomingMessageHandler: [<EmberIncomingMessageType.INCOMING_UNICAST: 0>, EmberApsFrame(profileId=260, clusterId=2820, sourceEndpoint=1, destinationEndpoint=1, options=<EmberApsOption.APS_OPTION_ENABLE_ROUTE_DISCOVERY: 256>, groupId=0, sequence=121), 254, -82, 0xdf10, 255, 255, b'\x18\xc0\n\x05\x05!\x92\x04']
2023-12-28 14:05:17.845 DEBUG (MainThread) [bellows.zigbee.application] Received incomingMessageHandler frame with [<EmberIncomingMessageType.INCOMING_UNICAST: 0>, EmberApsFrame(profileId=260, clusterId=2820, sourceEndpoint=1, destinationEndpoint=1, options=<EmberApsOption.APS_OPTION_ENABLE_ROUTE_DISCOVERY: 256>, groupId=0, sequence=121), 254, -82, 0xdf10, 255, 255, b'\x18\xc0\n\x05\x05!\x92\x04']
2023-12-28 14:05:17.845 DEBUG (MainThread) [zigpy.application] Received a packet: ZigbeePacket(timestamp=datetime.datetime(2023, 12, 28, 20, 5, 17, 845700, tzinfo=datetime.timezone.utc), src=AddrModeAddress(addr_mode=<AddrMode.NWK: 2>, address=0xDF10), src_ep=1, dst=AddrModeAddress(addr_mode=<AddrMode.NWK: 2>, address=0x0000), dst_ep=1, source_route=None, extended_timeout=False, tsn=121, profile_id=260, cluster_id=2820, data=Serialized[b'\x18\xc0\n\x05\x05!\x92\x04'], tx_options=<TransmitOptions.NONE: 0>, radius=0, non_member_radius=0, lqi=254, rssi=-82)
2023-12-28 14:05:17.847 DEBUG (MainThread) [zigpy.zcl] [0xDF10:1:0x0b04] Received ZCL frame: b'\x18\xc0\n\x05\x05!\x92\x04'
2023-12-28 14:05:17.847 DEBUG (MainThread) [zigpy.zcl] [0xDF10:1:0x0b04] Decoded ZCL frame header: ZCLHeader(frame_control=FrameControl(frame_type=<FrameType.GLOBAL_COMMAND: 0>, is_manufacturer_specific=0, direction=<Direction.Client_to_Server: 1>, disable_default_response=1, reserved=0, *is_cluster=False, *is_general=True), tsn=192, command_id=10, *direction=<Direction.Client_to_Server: 1>)
2023-12-28 14:05:17.849 DEBUG (MainThread) [zigpy.zcl] [0xDF10:1:0x0b04] Decoded ZCL frame: ElectricalMeasurement:Report_Attributes(attribute_reports=[Attribute(attrid=0x0505, value=TypeValue(type=uint16_t, value=1170))])
2023-12-28 14:05:17.849 DEBUG (MainThread) [zigpy.zcl] [0xDF10:1:0x0b04] Received command 0x0A (TSN 192): Report_Attributes(attribute_reports=[Attribute(attrid=0x0505, value=TypeValue(type=uint16_t, value=1170))])
2023-12-28 14:05:17.850 DEBUG (MainThread) [zigpy.zcl] [0xDF10:1:0x0b04] Attribute report received: rms_voltage=1170
2023-12-28 14:05:17.852 DEBUG (MainThread) [serialpy.descriptor_transport] Immediately writing b'\x82P:~'
2023-12-28 14:05:17.853 DEBUG (MainThread) [serialpy.descriptor_transport] Sent 4 of 4 bytes
...

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (09b2782) 99.78% compared to head (94e0e6e) 99.81%.

Additional details and impacted files

@@            Coverage Diff             @@
##              dev     #604      +/-   ##
==========================================
+ Coverage   99.78%   99.81%   +0.02%     
==========================================
  Files          67       68       +1     
  Lines        4728     4817      +89     
==========================================
+ Hits         4718     4808      +90     
+ Misses         10        9       -1     

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