ci: improved check-coverage action

[benceharomi]

Description

Added PR commenting functionality to the check-coverage GitHub action (post a comment with the result of the code coverage check to an opened PR).

Functional requirements

• The GitHub action is capable of adding a comment with the result of coverage check (percentage, percentage threshold, #lines covered)
• The GitHub action is capable of updating the previous comment it posted (to not spam the PR with comments after each change)

Testing requirements

Test passing coverage checks (these are tested in PR #3):

• coverage check passes -> action successful -> result commented
• success comment updated with fail comment
• success comment updated with success comment (with different %)

Test failing coverage checks (these are tested in PR #4):

• coverage check fails -> action unsuccessful -> result commented
• fail comment updated with success comment
• fail comment updated with fail comment (with different %)

[github-actions]

📊 Coverage Report

Metric	Coverage	Required	Status
Lines	100.00%	90%	✅ Above threshold

Details: 4 of 4 lines covered.