pd: use commit_in_place to write app safeguard

[erwanor]

Describe your changes

This PR:

• fixes a bug in the app version safeguard logic that would cause discrepancies between JMT state versions and block height
• refactors some of the inner logic to avoid writing any state unless it is necessary (i.e, no safeguard was found)

Testing this:

To observe the state discrepancy and test remediation:

1. Checkout the commit that only contains the extra tracing statement: git checkout a8c51f0cacb64304a6b1781226d6f74376800af7
2. Create a local devnet
3. Restart the devnet N times
4. Observe that the state version and block height have offset=N

To test that this fixes it:

1. Run this patch
2. Restart the node
3. Observe that the state version stays stable.

Checklist before requesting a review

• I have added guiding text to explain how a reviewer should test these changes.

• If this code contains consensus-breaking changes, I have added the "consensus-breaking" label. Otherwise, I declare my belief that there are not consensus-breaking changes, for the following reason:

  Not consensus breaking.

[conorsch]

Refs #4919.

[conorsch]

Thanks for the test plan, made it simple to verify the fix. 🙏