[store] feature: add SledVarTypeTree to store more than one types of key-value in one sled::Tree.

[drmingdrmer]

I hereby agree to the terms of the CLA available at: https://datafuse.rs/policies/cla/

Summary

[store] feature: add SledVarTypeTree to store more than one types of key-value in one sled::Tree.

SledVarTypeTree is a candidate as raft state machine store.
Storing all state(such as last applied log index or internal seq number counter) in one tree makes transactional update or snapshot creation much easier.

Changelog

• New Feature

Related Issues

#271

#1080

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[codecov-commenter]

Codecov Report

Merging #1181 (8a9ae22) into master (a8b1682) will increase coverage by 0%.
The diff coverage is 94%.

@@           Coverage Diff           @@
##           master   #1181    +/-   ##
=======================================
  Coverage      70%     71%            
=======================================
  Files         443     446     +3     
  Lines       25799   26330   +531     
=======================================
+ Hits        18215   18713   +498     
- Misses       7584    7617    +33     

Impacted Files	Coverage Δ
fusestore/store/src/meta_service/state_machine.rs	90% <ø> (ø)
fusestore/store/src/meta_service/raft_types.rs	75% <60%> (-25%)	⬇️
...estore/store/src/meta_service/sled_vartype_tree.rs	91% <91%> (ø)
fusestore/store/src/meta_service/sledkv.rs	94% <94%> (ø)
...e/store/src/meta_service/sled_vartype_tree_test.rs	96% <96%> (ø)
common/runtime/src/runtime_test.rs	53% <0%> (-21%)	⬇️
...pelines/transforms/transform_aggregator_partial.rs	87% <0%> (-2%)	⬇️
fusestore/store/src/meta_service/raftmeta.rs	78% <0%> (ø)
... and 1 more

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