Update set_partial_values to accept Buffer rather than BytesLike

[maxrjones]

When working on #2614 in https://github.com/maxrjones/zarr-python/tree/testing-storage, I found that the current implementation of set_partial_values for local store cannot work as written because it passes BytesLike to _put which expects a buffer. None of the other stores implement set_partial_values, so it's not possible to look to them for the correct way of implementing this method.

I believe that one of the following needs to happen in order for stores to correctly implement set_partial_values:

• Add a prototype argument to set_partial_values that can be used to go from BytesLike -> Buffer
• Update set_partial_values to accept Buffer types rather than BytesLike types

I chose the second option for this PR because all the other set methods seem to accept Buffer types. Of course, I welcome corrections if I am not understanding something here and the function signature should work as-is.

[maxrjones]

set_partial_values for a LocalStore requires that a key exist. This test assumes this is the intended behavior and creates a key containing no data prior to testing set_partial_values.

[maxrjones]

I'm realizing this may be wrong. I interpreted supports_partial_writes to refer to whether set_partial_values is implemented whereas it may actually refer to whether set includes a byte_range parameter. I am not sure which, if either, is correct because MemoryStore had supports_partial_writes=True with byte_range implemented for set but no implemented set_partial_values whereas LocalStore had supports_partial_writes=True with no byte_range implemented for set but included a set_partial_values implementation.