POLY_1271: order signer always set to EOA instead of funder (deposit wallet)

[31415man]

Bug: For EIP-7702 deposit wallet accounts (new system since April 2026),
create_and_post_order() always sets order.signer = EOA instead of funder (deposit wallet).

Error: "the order signer address has to be the address of the API KEY"

Setup:

• EOA: 0x8C1336d64920F36253fE56D377245d0f77F1B622
• Deposit Wallet: 0x3704F29C3cc19B4668Ff4DC670fb55309403B199
• signature_type=3 (POLY_1271)

Root cause: In build_market_order():
signer=self.signer.address() # always EOA
Should be:
signer=self.funder if self.signature_type == POLY_1271 else self.signer.address()

Workaround: None found.