HAMSTR-813 auto release on arbitrated release

[HQS-Gun]

Motivation

In the new arbitration logic, the lifecycle of arbitration goes like this:
Proposal
A buyer or seller submits a proposal to either refund (to payer) or release (to receiver) a specific amount. At that point, it’s just a proposal.
Voting
Arbiters (those who are registered as arbiters for the escrow) vote on the proposal. When it reaches a certain number of ‘yes’ votes, it’s automatically set to “ACCEPTED” status. But it isn’t executed at that point.
Execution
Anyone can execute a proposal, IF it’s been accepted (if it’s status is ACCEPTED, that is). But it’s a separate step… if nobody calls the execute method on the arbitration module, then the effect of the accepted proposal never takes effect.

Changes:

1. Add autoExecute boolean property to ArbitrationProposal struct
2. Update proposeArbitration() function to accept autoExecute parameter
3. Implement auto-execution logic in voteArbitration() when proposal becomes ACCEPTED
4. Add executeArbitrationProposal() method to PolyEscrow for ArbitrationModule to call
5. Update all existing test calls to include new autoExecute parameter

Test:

1. testAutoExecuteFalse() - Verifies proposals with autoExecute=false become ACCEPTED but don't auto-execute
2. testAutoExecuteTrue() - Verifies proposals with autoExecute=true automatically execute when ACCEPTED
3. Run forge test --match-contract AutoExecuteTest to verify both behaviors work correctly.