LTI1p3: update timezone handling to accomodate Canvas change

[ascholerChemeketa]

This pull request enhances the handling of assignment due dates received from LTI integrations by improving timezone awareness and ensuring due dates are accurately converted to the course's local time. The changes also update function signatures to pass the course object where needed for timezone conversion.

Timezone handling improvements:

• The update_rsassignment_from_lti function now normalizes ISO datetime strings with trailing "Z" (UTC) and, if both the incoming due date and the course have timezone information, converts the due date to the course's local timezone using ZoneInfo. Logging has been added for better traceability.

Function signature and import updates:

• The update_rsassignment_from_lti function signature is updated to accept a course parameter, and all calls to this function in launch and assign_select are updated accordingly. [1] [2]
• The Courses model and ZoneInfo are imported to support the new timezone logic. [1] [2]