Add replacement APIs for methods we intend to deprecate.

[cody-littley]

Describe your changes and provide context

Adds new methods to the top level Committer interface. The goal is to eventually deprecate the child CommitKVStore interface, and these new methods are a step in that direction.

type Committer interface {
    // ...
    Get(store string, key []byte) (value []byte, ok bool, err error)
    Has(store string, key []byte) (bool, error)
    Iterator(store string, start []byte, end []byte, ascending bool) (dbm.Iterator, error)
    GetProof(store string, key []byte) (*ics23.CommitmentProof, error)
    // ...
}

Testing performed to validate your change

Unit tests. These methods are not yet invoked in any production pathways.

[github-actions]

The latest Buf updates on your PR. Results from workflow Buf / buf (pull_request).

Build	Format	Lint	Breaking	Updated (UTC)
✅ passed	✅ passed	✅ passed	✅ passed	May 6, 2026, 3:14 PM

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 59.13%. Comparing base (68b9eeb) to head (0939d8d).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3397      +/-   ##
==========================================
+ Coverage   59.03%   59.13%   +0.09%     
==========================================
  Files        2102     2101       -1     
  Lines      173237   173273      +36     
==========================================
+ Hits       102277   102463     +186     
+ Misses      62083    61933     -150     
  Partials     8877     8877              

Flag	Coverage Δ
sei-chain-pr	75.63% <100.00%> (?)
sei-db	70.41% <ø> (ø)

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

Files with missing lines	Coverage Δ
sei-db/state_db/sc/composite/store.go	74.12% <100.00%> (+5.33%)	⬆️
sei-db/state_db/sc/memiavl/store.go	93.49% <100.00%> (+2.79%)	⬆️

... and 29 files with indirect coverage changes

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