CasObject + LocalClient

[rajatarya]

cas_object crate with cas_client/local_client.rs updated to use cas_object crate.

All unit-tests pass.

Next up is remote_client.rs, but this should bring new CAS Object format into xet-core.

[rajatarya]

Most of this code has been reviewed in the xetpoc-monorepo but has been adapted so it can fit into this repo (crates moved around, creating CasObjectError).

Happy to walk through this code since the changes all appear new. Just let me know.

Relevant PRs:

• https://github.com/huggingface-internal/xetpoc-monorepo/pull/5
• https://github.com/huggingface-internal/xetpoc-monorepo/pull/10

[rajatarya]

I recommend looking at local_client.rs - it is the main glue between cas_object_format.rs and the rest of cas_client crate.

[seanses]

LGTM! Can you rebase off the latest main and let the CI run and check?