Add clean up for Polygon ephemeral account

Context

Due to the big overestimation we are doing for the maxFeePerGas and maxPriorityFeePerGas parameters of the squidrouter transactions, the RPC nodes require the ephemeral account to have a lot more of the native token than required. At the moment, we are not returning the native tokens that were sent by the funding account, back to the funding account. This is mostly relevant for the EUR onramp flow as this is the only route that requires a squidrouter transaction from Polygon.

TODO

Add a cleanup transaction for the Polygon ephemeral account and make it automatically execute by the cleanup worker.

Challenges

• Permit/approve doesn't work because it's not an ERC20
• Look into alternative ways to pay gas for this account

Idea: Create a cleanup transaction for specific amount. Maybe have the funding account send so much POL so that the specified amount is reached and the presigned cleanup can properly execute.

Start by tracing the Polygon ephemeral-account funding flow and the cleanup worker, focusing on how squidrouter transactions are prepared and executed. Determine a viable way to return native tokens when permit/approve cannot be used, then confirm that the cleanup transaction runs automatically and returns the intended funds to the funding account.