refactor(storage): remove lifetime on Iter in StateStore

[lmatz]

What's changed and what's your intention?

This is useless as we have removed all the lifetime on user iterators.

This is the first step for #2221 to replace scan with iter.

[codecov]

Codecov Report

Merging #2235 (b9933bd) into main (08b2ec9) will decrease coverage by 0.08%.
The diff coverage is 33.33%.

@@            Coverage Diff             @@
##             main    #2235      +/-   ##
==========================================
- Coverage   70.96%   70.88%   -0.09%     
==========================================
  Files         657      657              
  Lines       83050    83141      +91     
==========================================
- Hits        58938    58932       -6     
- Misses      24112    24209      +97     

Flag	Coverage Δ
rust	70.88% <33.33%> (-0.09%)	⬇️

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% <ø> (ø)
src/storage/src/memory.rs	80.00% <ø> (ø)
src/storage/src/monitor/monitored_store.rs	2.81% <0.00%> (ø)
src/storage/src/panic_store.rs	0.00% <ø> (ø)
src/storage/src/rocksdb_local_mock.rs	0.00% <ø> (ø)
src/storage/src/store.rs	100.00% <ø> (ø)
src/storage/src/tikv_mock.rs	0.00% <ø> (ø)
src/storage/src/keyspace.rs	90.17% <100.00%> (ø)
...ntend/src/optimizer/plan_node/stream_delta_join.rs	48.57% <0.00%> (-18.85%)	⬇️
src/connector/src/utils.rs	74.02% <0.00%> (-6.26%)	⬇️
... and 18 more

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[BugenZhao]

LONG EXPECTED!!!