Giving Rust a chance for in-kernel codecs

My next step is to set up some infrastructure to test this continuously. If regressions can be quickly pinpointed and acted upon, we will be in a really good place to move forward with Rust in other fragile parts of the media code. This also applies to frameworks as well, like videobuf2 and mem2mem.

I've started discussions on a new iteration of mem2mem[0]. It's clear to me that it can be written in Rust directly by providing a C API through cbindgen. The framework can switch to C when executing any callbacks implemented by the driver, while drivers themselves keep their C code intact, if they so desire.

[0] - https://lore.kernel.org/linux-media/3F80AC0D-DCAA-4EDE-BF...