Feature: merge buy & edit cover in a single function and remove refund logic from Cover

[shark0der]

Context

Partial implementation of #386.

Changes proposed in this pull request

• Given the logic overlap between buyCover and editCover the PR merges them in a single function
• Removes the refund logic from the Cover contract in order to avoid cross-pool refund (buy on staking pool X, move cover to Y hence switching the rewards from one pool to another and "rugging" the stakers)
• Moves the following items from the CoverUtilsLib to Cover contract:
  • payment handling
  • stake burn function
  • stakingPool function

Test plan

All buyCover tests failed and need fixing (TBD).

Checklist

• Attached corresponding Github issue
• Prefixed the name with the type of change (i.e. feat, chore, test)
• Performed a self-review of my own code
• Made corresponding changes to the documentation
• Didn't generate new warnings
• Added tests that prove my fix is effective or that my feature works

Review

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• 🔨 = I believe this should be changed.
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• 🚀 = Feedback

[danoctavian]

would rename this to poolAllocationRequests

The fact that there is another type called AllocationRequest makes it hard to disambiguate between what's coming from that array and what's being created inside the pool