[esp-storage]: Add ability to Read/Write flash using embedded-io::{Read, Write}

[AnthonyGrondin]

Motivations

Currently esp-storage implements embedded_storage::{ReadStorage, Storage} to read and write to flash storage, but those traits take a slice as input. Let's say a user wants to write a large amount of bytes (> 20k for example), from a data structure that needs serialization, this requires the user to create a whole copy of that data in memory, during serialization, before writing it.

Considering that reading directly from flash would still require a slice to be passed for the bytes to be stored, optimization is more about writing.

Some implementations, such as postcard offer an API to Serialize / De-serialize directly from implementers of embedded-io::{Read, Write}.

Solution

Implement more traits for FlashStorage to allow reading and writing from types implementing embedded-io::{Read, Write} traits

Alternatives

N/A

Additional context

• postcard::to_eio<T, W>(value: &T, writer: W) -> Serialize a T to an embedded_io Write
• postcard::from_eio<'a, T, R>(val: (R, &'a mut [u8])) -> Result<(T, (R, &'a mut [u8]))> -> Deserialize a message of type T from a embedded_io Read.