refactor: improve posts keeper input/output consistency

[dadamu]

Description

This PR improves posts keeper input and output consistency.

---

Author Checklist

All items are required. Please add a note to the item if the item is not applicable and please add links to any relevant follow up issues.

I have...

• [x] included the correct type prefix in the PR title
• [ ] added ! to the type prefix if API or client breaking change
• [x] targeted the correct branch (see PR Targeting)
• [ ] provided a link to the relevant issue or specification
• [ ] followed the guidelines for building modules
• [ ] included the necessary unit and integration tests
• [ ] added a changelog entry to CHANGELOG.md
• [ ] included comments for documenting Go code
• [ ] updated the relevant documentation or specification
• [x] reviewed "Files changed" and left comments if necessary
• [ ] confirmed all CI checks have passed

Reviewers Checklist

All items are required. Please add a note if the item is not applicable and please add your handle next to the items reviewed if you only reviewed selected items.

I have...

• [ ] confirmed the correct type prefix in the PR title
• [ ] confirmed ! in the type prefix if API or client breaking change
• [ ] confirmed all author checklist items have been addressed
• [ ] reviewed state machine logic
• [ ] reviewed API design and naming
• [ ] reviewed documentation is accurate
• [ ] reviewed tests and test coverage
• [ ] manually tested (if applicable)

[codecov[bot]]

Codecov Report

Patch coverage is 60.00% of modified lines.

Files Changed	Coverage
app/app_config.go	ø
app/wasm_config.go	ø
x/posts/module.go	0.00%
x/posts/keeper/invariants.go	85.71%
app/app.go	100.00%
x/posts/abci.go	100.00%
x/posts/keeper/keeper.go	100.00%
x/posts/keeper/msg_server.go	100.00%
x/posts/wasm/querier.go	100.00%

:loudspeaker: Thoughts on this report? Let us know!.