Add tests to ensure temporary collection name formats don't change

mongomirror depends on recognizing specific temporary collection name patterns for correct operation:

• *.renameCollection
• tmp.agg_out.*
• tmp.mr.*

To ensure that future changes don't unexpectedly break mongomirror, we should confirm/add tests for these patterns, ideally with a warning comment not to change the formats without notifying the mongomirror team.