Add coverage profiling to unit tests and upload results to Codecov:

• Add -coverprofile flag to consensus tests (utils, common, x)
• Add -coverprofile flag to protocol tests (protocol, cache)
• Add codecov-action@v5 upload steps with flags for each test group
• Add explicit workflow permissions for checks and pull-requests
• Include coverage files in uploaded artifacts

Description

Closes: #XXXX

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...

• read the contribution guide
• included the correct type prefix in the PR title, you can find examples of the prefixes below:
• confirmed ! in the type prefix if API or client breaking change
• targeted the main branch
• provided a link to the relevant issue or specification
• reviewed "Files changed" and left comments if necessary
• included the necessary unit and integration tests
• updated the relevant documentation or specification, including comments for documenting Go code
• 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 all author checklist items have been addressed
• reviewed state machine logic, API design and naming, documentation is accurate, tests and test coverage