fix: duplicate token calls in batch escrow

[g4titanx]

summary

this fixes duplicate ERC20 calls in EscrowBatch when the reward asset is also one of the payment assets.

previously, the batch escrow handled reward and payment movements separately. that caused cases like USDC payment rows + USDC reward to produce two token calls: one for the reward and one for the payment bucket. the single ERC20 escrow already avoids this by moving reward + payment together.

changes

• fold reward into the matching asset bucket during _fund
• fold reward into the matching asset bucket during cancelAndWithdraw
• aggregate collect payouts by asset before sending funds to the bidder
• fold bond + rewardShare into the reward asset payout bucket
• add tests for one-call-per-token behavior