DRAFT: add standalone datastore service and client library

[vsaravind01]

Description

Added a standalone datastore service and client package under deepchem_server/services/datastore, including service API/auth layers and client HTTP/datastore abstractions. Also added tests and updated CI (core-pytests) to run deepchem_server/services/datastore/tests/.

• Follow-up PRs will wire core runtime paths to this client/service.

Type of change

Please check the option that is related to your PR.

• New feature (non-breaking change which adds functionality)
• Bug fix (non-breaking change which fixes an issue)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
  • In this case, we recommend to discuss your modification on GitHub issues before creating the PR
• Documentations (modification for documents)

Checklist

• Run lint.sh and ensure that it passes (Use ./lint.sh --fix to fix formatting issues automatically)
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• New unit tests pass locally with my changes
• I have checked my code and corrected any misspellings