Large documents in persistant memory

After implementing #12 it was discovered that larger GUI documents could not be stored in the persistant flash memory. This is due to a known limitation:

String values are currently limited to 4000 bytes. This includes the null terminator. Blob values are limited to 508,000 bytes or 97.6% of the partition size - 4000 bytes, whichever is lower.

This means that larger GUI documents than 4000 bytes are not going to be able to be stored upon uploading remotely.
The workaround for this is to hard-code the large GUI when compiling a sketch, and passing it to mgui_init().

This limitation is not necessarily a big issue that needs to be solved, but it could be a good idea to implement a smart workaround for this so that the user gets a better experience using MicroGUI.

Comienza revisando los límites de tamaño de la memoria flash NVS de ESP-IDF descritos en el issue y la ruta de carga de documentos alrededor de mgui_init(). Determina cómo se almacenan los documentos GUI cargados remotamente y define la finalización de modo que los documentos de más de 4000 bytes puedan almacenarse y utilizarse remotamente sin depender de sketches codificados de forma fija.