Remove attrs from V3

[normanrz]

In zarrita, I used attrs and cattrs for structuring the metadata and (de)serialization. However, it would be desirable to have less dependencies in zarr-python (see https://github.com/zarr-developers/zarr-python/pull/1583/files#r1420168951). We can use dataclasses instead and implement our own (de)serialization methods.

[jhamman]

xref: #1625

[d-v-b]

addressed in #1660