Add additional features to support SDF to Zarr conversion

[cwognum]

Changelogs

• Made it possible to use slices in pointers (e.g. path/to/data.zarr/col#0:10).
• Added the SDFConverter class to convert a SDF object to a Polaris Dataset.
• Started the implementation of a DatasetFactory as a unified system for creating datasets.
• Added the create_dataset_from_file utility method.
• Added Adapters to convert datapoints during data loading. These can be saved alongside a dataset.

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Checklist:

• Was this PR discussed in an issue? It is recommended to first discuss a new feature into a GitHub issue before opening a PR.
• Add tests to cover the fixed bug(s) or the newly introduced feature(s) (if appropriate).
• Update the API documentation if a new function is added, or an existing one is deleted.
• Write concise and explanatory changelogs above.
• If possible, assign one of the following labels to the PR: feature, fix or test (or ask a maintainer to do it for you).

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This PR started to add support for the MARCEL benchmark.

There were three critical changes to support MARCEL:

• We needed to convert a SDF file to Zarr, which we ended up doing using RDKit's bytestrings. See also the discussion Array-like structure for MolBlock IO rdkit/rdkit#7235
• We needed to allow for a variable number of conformers per datapoint, which we did by adding support for pointers with slice indexing (e.g. path/to/data.zarr/col#0:10)
• Allow users to specify an Adapter, which during data loading adapts the content saved in the Zarr file to a desired format (in this case, from a bytestring to a RDKit Mol object).

In addition, I long wanted to start on a system to make it easier to create dataset. I'm quite happy with this as a first version. It's a little crude still, but think it will be easy to extend as we work to make adding datasets more and more easy.

I added a tutorial and docstrings, but here is a short snippet:

from polaris.dataset import DatasetFactory
from polaris.dataset.converters import SDFConverter

# Create a new factory object
save_dst = "/path/to/destination.zarr
factory = DatasetFactory(zarr_root_path=save_dst)

# Register a converter for the SDF file format
factory.register_converter("sdf", SDFConverter())

# Process your SDF file
factory.add_from_file("/path/to/data.sdf")

# Build the dataset
dataset = factory.build()

[jstlaurent]

I'm a bit of my depth here, but that's some nice test coverage and I like concepts like pluggable converters.