* remote: Optimize traverse/no_traverse behavior
- estimate remote file count by fetching a single parent cache dir, then
determine whether or not to use no_traverse method for checking
remainder of cache entries in `cache_exists`
- thread requests when traversing full remote file lists (by fetching
one parent cache dir per thread)
* Use arbitrary prefix length for traverse remote cache queries
- default to 3
- for remotes that only support per-directory query use 2 (gdrive, hdfs)
* Add unit tests for new traverse/no_traverse behavior
* Fix deepsource warning
* Fix review issues
* fix CI
* Fix review issues
* obsolete no_traverse config option
- remove RemoteBASE.DEFAULT_NO_TRAVERSE and replace it with
RemoteBASE.CAN_TRAVERSE (True for all remotes except http)
* review issues - use 'object exists' instead of 'no_traverse'
* fix obsolete no_traverse test issues
* fix SSHMocked func tests