Add initial PlatformIO configuration and main application code

- Created platformio.ini for ESP32 Devkit configuration with DFPlayer Mini library dependency.
- Implemented main application logic in main.cpp, including LED and buzzer control, and MP3 playback functionality using DFMiniMp3 library.
- Added notification class for handling MP3 player events and errors.
- Set up input pins for buttons and output pins for LEDs, with synchronization logic.
- Included basic setup and loop functions to manage state and playback.
- Added README for test directory to outline unit testing purpose and resources.

.vscode/settings.json

@@ -0,0 +1,15 @@
+{
+    "python.autoComplete.extraPaths": [
+        "${workspaceFolder}/sources/poky/bitbake/lib",
+        "${workspaceFolder}/sources/poky/meta/lib"
+    ],
+    "python.analysis.extraPaths": [
+        "${workspaceFolder}/sources/poky/bitbake/lib",
+        "${workspaceFolder}/sources/poky/meta/lib"
+    ],
+    "files.associations": {
+        "*.dbclient-js": "javascript",
+        "*.conf": "bitbake",
+        "*.inc": "bitbake"
+    }
+}