mlokr has created PR #928: Fix session cursor retype in mongo-rust-driver

Issue Text:
Hello there,

when using the transaction API, I encountered unconditional panics and also panic while dropping in `SessionCursor::with_type`. The problem occurs because the `.state` is moved into new cursor and subsequently, `.unwrap()` is called on it when marking it exhausted and also when checking for exhaustion. This is the minimal code change to fix this problem