Function compress 

pub fn compress(data: &[u8], level: i32) -> Vec<u8> 

Compress data into a zstd frame.

level controls the compression strategy:

• 0: no compression (raw blocks, fastest)
• 1-2: greedy matching (fast, hash_log=14)
• 3-5: lazy matching (better ratio, hash_log=15)
• 6-8: lazy matching + deeper search (hash_log=16)
• 9-11: lazy matching + deepest search (hash_log=17)

Returns a valid zstd frame decompressible by any conformant decoder.