Feat/mvds00 run coinbase refactoring

[mvds00]

Description

Various minor tweaks to improve readability and performance of code. Fixes an issue where BlockEmission would be repeatedly set with wrong values.

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Other (please describe): cleanup

Checklist

• I have performed a self-review of my own code
• [-] I have commented my code, particularly in hard-to-understand areas
• I have run cargo fmt and cargo clippy to ensure my code is formatted and linted correctly
• [-] I have made corresponding changes to the documentation
• My changes generate no new warnings
• [-] I have added tests that prove my fix is effective or that my feature works
• [-] New and existing unit tests pass locally with my changes
• [-] Any dependent changes have been merged and published in downstream modules

Additional Notes

This is the first of a possible sequence of small PRs to refactor some subtensor code. This was discussed at OpenDev and in the new #refactor-run_coinbase discord channel.

[gztensor]

Not sure about moving this code to the different function:

        if BlockEmission::<T>::get() != block_emission_u64 {
            BlockEmission::<T>::put(block_emission_u64);
        }

Otherwise looks good.