Reimplement Random Number Generators

The random number generators previously implemented in pystencils.rng shall be re-designed and integrated with the pystencils 2.0 backend. This has three parts:

• Refactoring of the RNG front-end to integrate seamlessly with SymPy, using symbolic functions and array symbols
• Implementation of an IR representation for RNGs, parsing and type checking of front-end RNG expressions, lowering to platform-specific implementations, as well as vectorization
• Refactoring of the RNG runtime headers to improve integration with the IR

Progress

• RNG frontend, backend, and runtime infrastructure (!474 (merged), !481 (merged))
• Scalar Philox RNG (!474 (merged))
• Vectorized Philox RNG
• Scalar AES-NI RNG
• Vectorized AES-NI RNG