perf: remove dtype + fill val handling per chunk

[ilan-gold]

Calling to_native_dtype + __str__ came up as one of the only python-CPU-bound things when doing some benchmarking. My use-case is quite contrived (generating thousands of WithSubset objects) but I think it's probably worth investigating getting rid of these calls. Some observations:

1. I wonder if all getting the dtype and fill_val be wrapped up in just relying on https://docs.rs/zarrs/latest/zarrs/array/struct.Array.html#method.open and then using the values directly (there are probably other benefits of doing this) but I think this is a separate PR So it turns out the array actually doesn't have to be created yet when the pipeline is generated. So I ended up doing something similar with the metadata (making it an actual Struct and then working with that to get fill and dtype).
2. Regardless, most of this refactor is around removing Basic anyway so that chunk handling is independent of the ability. I noticed that ChunkRepresentation requires ownership over its arguments which means we copy per-chunk. Not sure what would go into making that a reference, but it's no worse than the previous situation where I think we were generating copies repeatedly, but from PyO3 calling python --> Hooray! No longer!

The benefit wasn't crazy ~5% but I think going in this direction is good (see point 1)

[ilan-gold]

@LDeakin Up to you if we wait for 0.23.1. Thanks for the help here!

[ilan-gold]

Locally I'm getting "DataTypeMetadataV2 doesn't implement std::fmt::Display" which seems incorrect based on https://github.com/zarrs/zarrs/blob/0b36a73f861bc8189ba4cde315630d828db3de80/zarrs_metadata/src/v2/array.rs#L190. Sorry about that

[LDeakin]

Locally I'm getting "DataTypeMetadataV2 doesn't implement std::fmt::Display" which seems incorrect based on https://github.com/zarrs/zarrs/blob/0b36a73f861bc8189ba4cde315630d828db3de80/zarrs_metadata/src/v2/array.rs#L190. Sorry about that

Just run a cargo update and you'll get the latest release of zarrs_metadata

[LDeakin]

Nice one Ilan! I might rerun some perf benchmarks with this after we release

[ilan-gold]

Just run a cargo update and you'll get the latest release of zarrs_metadata

Tried that out but oddly enough didn't work. I'm cycling through the other options available but at least I see this is a local-only problem now, so I'll handle it.