INTPYTHON-825 LangGraph-Checkpoint CVE fix

[caseyclements]

Issue Key

Summary

This PR addresses a critical security vulnerability found in langgraph-checkpoint's serializer, "JsonSerializer". It is described in detail here: RCE in json mode of JsonPlusSerializer.

Changes in this PR

The primary change was to bump to "langggraph-checkpoint >= 3.0".
The base checkpointer removed dumps/loads in preference of typed versions. We had previously only used the defaults so a few changes were made to update to these.

Test Plan

This change does not change any of our API so no changes to tests were made. All pass. INTPYTHON-826 will add tests of the serialization types once we expose them.

Screenshots (optional)

Checklist

Checklist for Author

• Did you update the changelog (if necessary)?
• Is the intention of the code captured in relevant tests?
• Has a MongoDB Employee run the patch build of this PR?

Checklist for Reviewer {@primary_reviewer}

• Does the title of the PR reference a JIRA Ticket?
• Do you fully understand the implementation? (Would you be comfortable explaining how this code works to someone else?)
• Have you checked for spelling & grammar errors?
• Is all relevant documentation (README or docstring) updated?

[caseyclements]

Passing Evergreen Patch Build

[blink1073]

LGTM!