ZSTD decoder: cocotb utils and decoder testcases, verilog helper modules

[rw1nkler]

Added functionality:

• multiple testcases covering the decoding of frames with "compressed" blocks of different type
• cocotb testing utilities for common operations on XLS channels
• collection of PnR benchmarks
• ZSTD frame generator
• tests of axi ram writer/reader procs as well as memreader & memwriter

Supersedes #2717

[rw1nkler]

@proppy Please let us know if there’s anything else we can do to move this forward

[proppy]

Marking this as draft until it's ready to review again.