[uart] Keep constant switch, button and write payloads in flash (#20082)

tests/component_tests/uart/config/payload_tables.yaml

@@ -0,0 +1,34 @@
+---
+esphome:
+  name: test
+  on_boot:
+    then:
+      - uart.write: [0x01, 0x02, 0x03]
+      - uart.write: !lambda return {0x09};
+      - uart.write: ""
+
+esp32:
+  board: esp32dev
+
+uart:
+  tx_pin: 17
+  rx_pin: 16
+  baud_rate: 9600
+
+switch:
+  - platform: uart
+    id: shared_switch
+    name: Shared Switch
+    data: [0x01, 0x02, 0x03]
+  - platform: uart
+    id: on_off_switch
+    name: On Off Switch
+    data:
+      turn_on: "ON"
+      turn_off: [0x04]
+
+button:
+  - platform: uart
+    id: shared_button
+    name: Shared Button
+    data: [0x01, 0x02, 0x03]

tests/component_tests/uart/test_payload_tables.py

@@ -0,0 +1,28 @@
+"""Tests for UART constant payloads in shared PROGMEM tables."""
+
+from collections.abc import Callable
+from pathlib import Path
+import re
+
+
+def test_constant_payloads_share_progmem_tables(
+    generate_main: Callable[[str | Path], str],
+    component_config_path: Callable[[str], Path],
+) -> None:
+    """Equal payloads share one table across switch, button and write action."""
+    main_cpp = generate_main(component_config_path("payload_tables.yaml"))
+
+    tables = dict(
+        re.findall(
+            r"static constexpr uint8_t (\w+)\[\] PROGMEM = (\{[^}]*\});", main_cpp
+        )
+    )
+    shared = next(k for k, v in tables.items() if v == "{0x01, 0x02, 0x03}")
+    assert sorted(tables.values()) == sorted(
+        ["{0x01, 0x02, 0x03}", "{0x4F, 0x4E}", "{0x04}"]
+    )
+    assert f"shared_switch->set_data_on({shared}, 3);" in main_cpp
+    assert f"shared_button->set_data({shared}, 3);" in main_cpp
+    assert f"set_data_static({shared}, 3);" in main_cpp
+    assert "set_data_static(nullptr, 0);" in main_cpp
+    assert "set_data_template(" in main_cpp