chore: improve ES Check type inference

[kylezs]

Pull Request

Checklist

Please conduct a thorough self-review before opening the PR.

• [x] I am confident that the code works.
• [x] I have written sufficient tests.
• [x] I have written and tested required migrations.
• [x] I have updated documentation where appropriate.

Summary

I hit an issue when writing a check like so on my PR:

number_of_open_elections_is(_pre, post, n: ElectionCount) {
    assert_eq!(post.unsynchronised_state.open_elections, n, "Number of open elections should be {}", n);
},

and it was because without explicitly comparing the whole post-state as is currently done on some Checks, it can't infer the rest of the state. Fixing this by explicitly providing the type in the closure, writing checks should remain just as clean.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 72%. Comparing base (277b152) to head (f3eee8d). Report is 7 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #5448 +/- ## ====================================== - Coverage 72% 72% -0% ====================================== Files 490 490 Lines 87053 86929 -124 Branches 87053 86929 -124 ====================================== - Hits 62423 62242 -181 - Misses 21675 21729 +54 - Partials 2955 2958 +3 ```

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