Reusing context for compression

[nono303]

Actually, ZSTD_createCCtx() is called on compress_filter (output filter registered function)
This implies that the zstd context is created and destroyed on each request - which might not be optimized for performance.

https://facebook.github.io/zstd/zstd_manual.html#chapter4

When compressing many times,
  it is recommended to allocate a context just once,
  and re-use it for each successive compression operation.
  This will make workload friendlier for system's memory.
  Note : re-using context is just a speed / resource optimization.
         It doesn't change the compression ratio, which remains identical.
  Note 2 : In multi-threaded environments,
         use one different context per thread for parallel execution.

Also Cf. facebook/zstd#2107

So, my question is, could the zstd context can be instantiated one time by "worker ❓" and reused for all compression process.
⚠ Must be thread safe in case of concurrent compression in a given worker