skip extend reservation vote when reservation already expired

[nudiltoys-cmyk]

summary

I noticed _try_extend_reservation fires vote_extend_reservation even when the miner's reservation has already lapsed. the condition reserved_until < current_block + EXTEND_THRESHOLD_BLOCKS is true for any reserved_until behind current_block, so expired reservations trigger a contract call that gets rejected with NoReservation

changed the guard to 0 < blocks_left < EXTEND_THRESHOLD_BLOCKS so it only fires when the reservation is still alive but within the threshold window

test plan

verified the condition against blocks_left values of -5, 0, 1, 19, 20, 21, only 1 through 19 should trigger the extend vote

[LandynDev]

hey — appreciate the eye on this, but this one's been overtaken by the post-v1 refactor in #46 and #47

• already prevented upstream — state_store.purge_expired_pending_confirms() at forward.py:44 drops expired pending_confirms before try_extend_reservation is even reached, so the blocks_left ≤ 0 path you're guarding shouldn't be hit in normal flow anymore.