Streamline the implementation of collect and caching in readers

[hunterhector]

Is your feature request related to a problem? Please describe.
The design of collect and cache_key_function is to help develop a caching function during data reading. This design expects the users to cache the results of collect. and use the cache_key to retrieve it. But this creates the following problem:

1. If one does not want to develop caching, this design is confusing and cumbersome to them. Even worse, they will arbitrarily implement these functions, which are not effective for caching, providing bad examples for future adopters.
2. The test coverage for these is not enough.

Describe the solution you'd like

1. We probably need to provide two ways to implement readers: a simple reader, or a reader with some caching ability.
2. as requested several times, some base class for reader tests should be implemented, that automatically test these function branches (e.g. caching).
3. And we should provide standard implementations for readers.

Describe alternatives you've considered

Additional context
Some issues are related to this, such as this one: #239