fix(state-store): fix a full key compare bug in state store get

[BowenXiao1999]

What's changed and what's your intention?

PLEASE DO NOT LEAVE THIS EMPTY !!!

Please explain IN DETAIL what the changes are in this PR and why they are needed:

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• How does this PR work? Need a brief introduction for the changed logic (optional)
• Describe clearly one logical change and avoid lazy messages (optional)
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Checklist

• I have written necessary docs and comments
• I have added necessary unit tests and integration tests

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[BowenXiao1999]

Still strange. We need to construct a FullKey and immediately consume it. A lot of copy here

[skyzh]

I'd like to have a FullKeySlice structure here. https://github.com/dtolnay/ref-cast may help to convert &[u8] into a FullKeySlice.

[BowenXiao1999]

I think it do not works. Refcast only accept one parameters like &[u8]. However, we get epoch and userkey (&[u8]). No idea how to concatenate them..

[codecov]

Codecov Report

Merging #2237 (323575f) into main (20c355e) will increase coverage by 0.14%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #2237      +/-   ##
==========================================
+ Coverage   70.88%   71.02%   +0.14%     
==========================================
  Files         657      657              
  Lines       83141    83592     +451     
==========================================
+ Hits        58936    59375     +439     
- Misses      24205    24217      +12     

Flag	Coverage Δ
rust	71.02% <100.00%> (+0.14%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
src/storage/src/hummock/state_store.rs	71.93% <100.00%> (ø)
src/expr/src/vector_op/agg/general_distinct_agg.rs	65.57% <0.00%> (-2.52%)	⬇️
...c/expr/src/vector_op/agg/general_sorted_grouper.rs	91.21% <0.00%> (-1.88%)	⬇️
src/connector/src/filesystem/file_common.rs	80.00% <0.00%> (-0.89%)	⬇️
src/common/src/types/ordered_float.rs	24.10% <0.00%> (-0.20%)	⬇️
src/batch/src/executor/mod.rs	60.46% <0.00%> (ø)
src/batch/src/executor2/mod.rs	100.00% <0.00%> (ø)
src/expr/src/vector_op/agg/aggregator.rs	89.81% <0.00%> (ø)
src/batch/src/executor/sort_agg.rs
src/batch/src/executor2/sort_agg.rs	93.12% <0.00%> (ø)
... and 2 more

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