ReadingRoomCache failover in multiple record situtation

[ctgraham]

Describe the bug

The api/reading-rooms endpoint does not gracefully handle multiple records in the ReadingRoomCache. The initial case of multiple records in this table was probably the result of a race condition.

To reproduce

Steps to reproduce the behavior:

1. Insert two records in process_request_readingroomcache in request broker's db.
2. GET api/reading-rooms
3. See error {"detail":"get() returned more than one ReadingRoomCache -- it returned 2!"}, UI renders no reading rooms.

Expected behavior

Exception is caught, best cached record is selected, and cache is scheduled to be cleared and rebuilt.

Error message or screenshots

n/a

Impact on your work

Presently, once multiple records are inserted, only manual intervention can clear them.

Additional context

PR incoming.

[helrond]

Closed by 030a994