* Code cleanup
`flush_queue()` is mostly used by tests
remove some unused params
avoid clones in a few places
* Consistent params naming
Consistent use of log calls
* Fix todo
It'a actually not trivial to find out the size of these collections, likely we keep blocks from all kinds of forks in the `self.blocks`/`self.parents` collections and there's no good way to anticipate how many blocks we're going to drain. Most of the time we end up draining 0 blocks and then we drain a whole bunch of them, up to 30 000.
* Revert making flush_queue() test-only
Address review grumbles
* More review grumbles
* fix build
9e77e7e193