Improve `#![no_std]` support - investigate removing all use of `alloc`

[mitchmindtree]

While we technically support #![no_std] today, however we still lean on alloc.

Many embedded applications don't support a global allocator at all - it would be nice to be able to support these. This might look like:

• Using something like heapless with fixed-size alternatives to the datastructures we currently use.
• Providing handy defaults (with generic sizes and types filled) to improve compilation speeds and UX for the common/std path.