Some parts of lib in no_std with alloc. Tests pass

[hatmajster]

This is ready, but not complete work, some things are still gated. I just tried to make it compile first, then for tests to pass. As it happened, here's the PR. I still have not used it in real product, and I did it blindly, so its a draft for now, though I don't expect much more work to be done here. Please verify carefully. Testing/review appreciated. I have no idea how to split this, organize etc. Any opinions, refactor ideas appreciated. I tried to not change as much code as possible, sometimes it doesn't make any sense, sometimes looks stupid. But essentially all commits should compile in some way using no_std and alloc features. PR requires this: https://github.com/Stoeoef/spade/pull/92, so you can see this dependency in Cargo.toml for now. If it will be merged, I'll change dependency here. As I wrote in the beginning I would like for this to not be full "no_std+alloc". Some parts are still gated. Its just a good start I hope, and if it gets merged I hope the rest may be done quickly. But I can of course add more if someone advise so. My main fear is that I just don't know if any of this actually works, so I would prefer to scope low.