Improve interface Python - Rust

[felixhekhorn]

• Identify weak points and improvements between numba and Rust
• Identify weak points and improvements between Python and numba and Rust
• Identify weak points and improvements between Rust/eko and Rust/ekore
• Implement improvements
• Update architecture documentation Document current architecture #516

Things to consider:

• build system
• passing numba function pointer around
• memory allocation and unravelling
• caching strategy
• more optimisation closer to hardware