feat(contracts): Add EntanglementManager

[lukmaan-ferrum]

This logic needs double checking:

Start

• Initially mint some qpBTC to get the system going
• Distribute this to some chosen initial stakers

Stakers staking

• Stakers call stakeQpBtc() to become stakers
• Their capacity is updated

Users bridging from L1 to ferrumnet (entangling)

• A random staker with enough capacity is chosen. A deposit address on L1 which corresponds to that staker is given to the user
• User sends BTC to this address
• Indexer pick this up and makes the tx available on ferrumnet, together with an encoded call to QP
• EntanglementManager reduces staker's capacity by the amount given to their BTC address
• EntanglementManager makes the QP call
• QP mints qpBTC to the user

Users bridging from ferrumnet to L1 (settling)
1/ Withdrawal request

• Request withdrawal
• EntanglementManager takes the QpBTC and stores in contract for now
• Random staker chosen to fulfill this withdrawal
• WithdrawalRequest event emitted
• Staker needs to listen for this event and fulfill withdrawal

2/ Verify withdrawal

• Once withdrawal is carried out on L1, call verifyWithdrawal(requestId, txHash)
• Check outputs address match that of user
• Increase staker capacity
• Burn QP

Stakers unstaking

• Can unstake up to their current capacity
  • Makes sure that staked qpBtc can only be withdrawn if it is not currently being use as collateral for minted qpBtc to some user

Known issues

• Small number of stakers can mean same staker chosen multiple times in same block, possible exceeding capacity
• Withdrawal request assumed staker can fullfil any amount of BTC during withdrawal