Add crc32c codec

[dstansby]

There's a request to add crc32c as a codec here, so zarr-python v3 can use it for sharding. I'm not entirely sure on the details, so someone more familiar might want to add a more in depth comment about this. More context at zarr-developers/zarr-python#2391

[normanrz]

Would we just declare crc32c as a dep here or compile the code within numcodecs?

[dstansby]

I'm pro adding it as a dependncy (and adding a corresponding Codec class for it)

[normanrz]

Should the codec append a checksum, as it does in zarr-python right now, or just compute the checksum (hard to decode, though)?