Have zigbee proxying piggyback off of serial proxying?

tests/components/zigbee_proxy/common.yaml

@@ -14,5 +14,10 @@ uart:
     rx_pin: ${rx_pin}
     baud_rate: 115200
 
-zigbee_proxy:
-  uart_id: zigbee_uart
+# The port owns the UART and carries every byte; zigbee_proxy only taps it
+serial_proxy:
+  - id: zigbee_serial
+    uart_id: zigbee_uart
+    name: Zigbee
+    port_type: TTL
+    mode: ezsp_ash

tests/components/zigbee_proxy/test-usb.esp32-s3-idf.yaml

@@ -15,7 +15,14 @@ usb_uart:
       - id: zigbee_usb_channel
         baud_rate: 460800
 
-# uart_id points at a USB UART channel; the component must detect this
-# automatically and enable the RX callback fast path (USE_ZIGBEE_PROXY_USB_UART)
+# The tapped port may be a USB CDC ACM channel just as well as a hardware UART:
+# zigbee_proxy never touches the UART itself, so it does not care which it is.
+serial_proxy:
+  - id: zigbee_usb_serial
+    uart_id: zigbee_usb_channel
+    name: Zigbee
+    port_type: TTL
+    mode: ezsp_ash
+
 zigbee_proxy:
-  uart_id: zigbee_usb_channel
+  serial_proxy_id: zigbee_usb_serial

tests/components/zigbee_proxy/test.esp32-idf.yaml

@@ -8,6 +8,7 @@ esp32:
 <<: !include common.yaml
 
 zigbee_proxy:
+  serial_proxy_id: zigbee_serial
   buffer_size: 1024
   initial_timeout: 1600
   min_timeout: 400

tests/components/zigbee_proxy/test.esp8266-ard.yaml

@@ -8,4 +8,5 @@ esp8266:
 <<: !include common.yaml
 
 zigbee_proxy:
+  serial_proxy_id: zigbee_serial
   buffer_size: 512

tests/components/zigbee_proxy/test.rp2040-ard.yaml

@@ -3,3 +3,6 @@ substitutions:
   rx_pin: GPIO1
 
 <<: !include common.yaml
+
+zigbee_proxy:
+  serial_proxy_id: zigbee_serial