pq: improve zstd by using shared contexts

[yaauie]

In #18121 we add support for ZSTD compression using the convenience methods com.github.luben.zstd.Zstd#decompress(byte[]) convenience method that does not require a-priori knowledge about the contents of the received byte[] or the expected decompressed size of the returned byte[], but carry the cost of instantiating a new com.github.luben.zstd.ZstdDecompressCtx for each usage instead of allowing the reuse of pooled resources.

This convenience method relies on private methods within com.github.luben.zstd.Zstd to scan the frames of the provided byte[] to determine the result buffer size, so that they can invoke methods on the reusable com.github.luben.zstd.ZstdDecompressCtx that require that foreknowledge.

This task is to explore the benefit of reusing ZstdDecompressCtx, which will entail:

• reimplementing those private methods from the BSD-2-licensed upstream project
• implementing a resource pool, using ThreadPool+Cleaner or similar
• analyzing the delta in performance and/or resource usage