Plutus V3 spend that consumes an Open escrow whose open_deadline has
elapsed and refunds every contributor. Same multi-output refund shape
as Veto, different validator gates: state==Open AND lower >
open_deadline_ms (strict gt). No required signer — time gate is the
only gate.
Reuses enterprise_address_for from escrow_veto. 5 tests: not-Open
reject, open-window-not-elapsed reject (off-by-one strict gt),
empty-escrow reject, two-contributor full refund happy path,
outsider driver works.
Closes the 5-redeemer escrow surface: open + deposit + agree + veto +
settle + refund_timeout. 35/35 escrow builder tests pass.
0feb0800dd