RingIO is limited to 64kB

Description

Discussion: https://github.com/micropython/micropython/pull/9458#issuecomment-2581252345

Currently RingIO is limited to creating ring buffers of 64kB by the use of the following uint16_t variables in ringbuf.h:

typedef struct _ringbuf_t {
    uint8_t *buf;
    uint16_t size;
    uint16_t iget;
    uint16_t iput;
} ringbuf_t;

The suggestion is to change these to uint32_t to allow for >64kB ringbuffers. This would only be useful in ports with more than 64kB of heap available, so it may be worthwhile having different versions for different ports.

Or maybe the extra 6 bytes is acceptable across all ports for the sake of simplicity/consistency?

I note that other structures (like bytearray) don't have a 64kB limit, so this would seem to be some sort of precedent for changing the limit.

Code Size

This change would add 6 bytes to RAM usage whenever RingIO is invoked

Implementation

I hope the MicroPython maintainers or community will implement this feature

Code of Conduct

Yes, I agree

Start in ringbuf.h and trace where ringbuf_t is allocated and used across the ports. Check how size, iget, and iput are represented and test whether buffers above 64kB work without exceeding port memory constraints; done means larger RingIO buffers are supported while the documented 6-byte RAM impact is addressed.