fix: add missing migration; use correct constant types (backport #1757)

[mergify]

Description

Closes: #1756

This PR adds missing migration for BlocksPerEpoch and fixes the bugs found in upgrade tests.

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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...

• Included the correct type prefix in the PR title
• Added ! to the type prefix if the change is state-machine breaking
• Confirmed this PR does not introduce changes requiring state migrations, OR migration code has been added to consumer and/or provider modules
• Targeted the correct branch (see PR Targeting)
• Provided a link to the relevant issue or specification
• Followed the guidelines for building SDK 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
• Reviewed "Files changed" and left comments if necessary
• Confirmed all CI checks have passed
• If this PR is library API breaking, bump the go.mod version string of the repo, and follow through on a new major release

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 ! the type prefix if the change is state-machine breaking
• confirmed this PR does not introduce changes requiring state migrations, OR confirmed migration code has been added to consumer and/or provider modules
• 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

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This is an automatic backport of pull request #1757 done by [Mergify](https://mergify.com).