feat(storage): remove FilterKeyExtractor trait for MultiFilterKeyExtractor

[Li0k]

Is your feature request related to a problem? Please describe. Currently, MultiFilterKeyExtractor is a struct that impletement FilterKeyExtractor trait. We can provide a nested structure with this implementation, but this is not safe. We want FilterKeyExtractor to be stateless, but now MultiFilterKeyExtractor needs to hold mutable self in order to maintain state. (For borrow checker, we use need a Mutex even if it wont be competing).

(https://github.com/singularity-data/risingwave/blob/main/src/storage/hummock_sdk/src/filter_key_extractor.rs) simple conclusion:

1. FilterKeyExtractor to be stateless
2. FilterKeyExtractor no needs to hold mutable self for maintaining state

Describe the solution you'd like

1. use a new struct FilterKeyExtractorContext to replace MultiFilterKeyExtractor which maintain state.
2. remove MultiFilterKeyExtractor for avoiding nested structure that it's uncontrollable
3. cached the last_filter_key_extractor_state for query optimization.
4. use separate FilterKeyExtractorContext for every compaction task split (Copy)

[ClSlaid]

May I take a look? I may be able to submit a PR next week...👀 Won't be fast...

[Li0k]

May I take a look? I may be able to submit a PR next week...👀 Won't be fast...

Thanks, you can self-assign

[ClSlaid]

1. FilterKeyExtractor to be stateless
2. FilterKeyExtractor no needs to hold mutable self for maintaining state

wait...? a stateless structure but need to maintain state?🤯