removed PrepareProposal from Application

[pompon0]

PrepareProposal in sei-chain Application is a noop, so I've removed it entirely to simplify the logic.

[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	Mar 24, 2026, 6:46 PM

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 58.69%. Comparing base (f7104d8) to head (1a5af0c).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3096      +/-   ##
==========================================
+ Coverage   58.58%   58.69%   +0.11%     
==========================================
  Files        2098     2093       -5     
  Lines      173649   172472    -1177     
==========================================
- Hits       101733   101239     -494     
+ Misses      62839    62284     -555     
+ Partials     9077     8949     -128     

Flag	Coverage Δ
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
app/app.go	67.60% <ø> (+0.16%)	⬆️
app/benchmark.go	48.93% <ø> (+4.10%)	⬆️
app/benchmark/benchmark.go	58.62% <ø> (-1.38%)	⬇️
app/benchmark/generator.go	42.51% <ø> (-3.33%)	⬇️
sei-cosmos/baseapp/abci.go	61.42% <ø> (+0.58%)	⬆️
sei-cosmos/baseapp/baseapp.go	74.14% <ø> (-0.47%)	⬇️
sei-cosmos/baseapp/options.go	59.49% <ø> (+0.23%)	⬆️
sei-tendermint/abci/types/application.go	48.38% <ø> (+13.50%)	⬆️
sei-tendermint/abci/types/mocks/application.go	13.12% <ø> (-2.36%)	⬇️
sei-tendermint/abci/types/plain_types.go	28.57% <ø> (+22.42%)	⬆️
... and 6 more

... and 75 files with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.