Improve code and documentation clarity for DataPipes APIs (#60423)
Summary:
Fixes issues that are discussed with ezyang in the comments of PR https://github.com/pytorch/pytorch/issues/59498
Improved code and documentation clarity, and refactored .filter to nesting_level directly
Pull Request resolved: https://github.com/pytorch/pytorch/pull/60423
Reviewed By: ezyang
Differential Revision: D29281599
Pulled By: NivekT
fbshipit-source-id: a9bbaf52f492db0741c00f3ceb4022b08ddb1506
