Epic: Stabilise unstable_encodings

[robert3005]

We have accumulated a list of interesting but unfinished array encodings. While they're grounded in concrete research and direction we want to go they're not quite as polished as we would like from encodings we would persist in files and commit to long term. However, there's more work required for all of them to resolve any outstanding questions and performance issues

Encodings

• OnPair
• Delta
• ZstdBuffers
• Tensor
• Patched (this has its own feature flag)

Unresolved questions

• zstd_buffers is strictly better for random access but worse for size, do we prefer it over regular zstd?