feat: locked yvUSD cooldown strategy and pending redemptions refactor

[johnnyonline]

Towards locked yvUSD market. Market oracle PR @ flexmeow/flex-contracts#24

[ctmotox2]

I was initially concerned that receiving the collateral and starting its cooldown in separate transactions could leave the accounting inconsistent between calls like an additional call may disrupt the accounting. Discussed with @johnnyonline , and both calls are executed atomically through the multisig, so this is not an issue. LGTM

[johnnyonline]

I was initially concerned that receiving the collateral and starting its cooldown in separate transactions could leave the accounting inconsistent between calls like an additional call may disrupt the accounting. Discussed with @johnnyonline , and both calls are executed atomically through the multisig, so this is not an issue. LGTM

Fixed that as well as Schlag's comment about pendingRedemptions may become outdated here