Import ESP_UniClock (upstream 1189810)

Vendored from https://github.com/gpeter62/ESP_UniClock: the sketch
source, the web UI and the libraries the ESP8266 build needs, unpacked
from the bundled zips. Adds a PlatformIO project for the ESP-12. The
source is unchanged; local changes follow as separate commits.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

firmware/uniclock/lib/PubSubClient/CHANGES.txt

@@ -0,0 +1,85 @@
+2.8
+   * Add setBufferSize() to override MQTT_MAX_PACKET_SIZE
+   * Add setKeepAlive() to override MQTT_KEEPALIVE
+   * Add setSocketTimeout() to overide MQTT_SOCKET_TIMEOUT
+   * Added check to prevent subscribe/unsubscribe to empty topics
+   * Declare wifi mode prior to connect in ESP example
+   * Use `strnlen` to avoid overruns
+   * Support pre-connected Client objects
+
+2.7
+   * Fix remaining-length handling to prevent buffer overrun
+   * Add large-payload API - beginPublish/write/publish/endPublish
+   * Add yield call to improve reliability on ESP
+   * Add Clean Session flag to connect options
+   * Add ESP32 support for functional callback signature
+   * Various other fixes
+
+2.4
+   * Add MQTT_SOCKET_TIMEOUT to prevent it blocking indefinitely
+     whilst waiting for inbound data
+   * Fixed return code when publishing >256 bytes
+
+2.3
+   * Add publish(topic,payload,retained) function
+
+2.2
+   * Change code layout to match Arduino Library reqs
+
+2.1
+   * Add MAX_TRANSFER_SIZE def to chunk messages if needed
+   * Reject topic/payloads that exceed MQTT_MAX_PACKET_SIZE
+
+2.0
+   * Add (and default to) MQTT 3.1.1 support
+   * Fix PROGMEM handling for Intel Galileo/ESP8266
+   * Add overloaded constructors for convenience
+   * Add chainable setters for server/callback/client/stream
+   * Add state function to return connack return code
+
+1.9
+   * Do not split MQTT packets over multiple calls to _client->write()
+   * API change: All constructors now require an instance of Client
+      to be passed in.
+   * Fixed example to match 1.8 api changes - dpslwk
+   * Added username/password support - WilHall
+   * Added publish_P - publishes messages from PROGMEM - jobytaffey
+
+1.8
+    * KeepAlive interval is configurable in PubSubClient.h
+    * Maximum packet size is configurable in PubSubClient.h
+    * API change: Return boolean rather than int from various functions
+    * API change: Length parameter in message callback changed
+       from int to unsigned int
+    * Various internal tidy-ups around types
+1.7
+    * Improved keepalive handling
+    * Updated to the Arduino-1.0 API
+1.6
+    * Added the ability to publish a retained message
+
+1.5
+    * Added default constructor
+    * Fixed compile error when used with arduino-0021 or later
+
+1.4
+    * Fixed connection lost handling
+
+1.3
+    * Fixed packet reading bug in PubSubClient.readPacket
+
+1.2
+    * Fixed compile error when used with arduino-0016 or later
+
+
+1.1
+    * Reduced size of library
+    * Added support for Will messages
+    * Clarified licensing - see LICENSE.txt
+
+
+1.0
+    * Only Quality of Service (QOS) 0 messaging is supported
+    * The maximum message size, including header, is 128 bytes
+    * The keepalive interval is set to 30 seconds
+    * No support for Will messages