Simplify seeder upload tracking

[diegomrsantos]

Summary

• replace the seeder upload bookkeeping with explicit scheduling and confirmation state
• clear out-of-order completions once the missing upload arrives and the frontier advances
• add a focused regression test for the out-of-order completion case

Root Cause

The previous seeder upload tracker modeled progress through an inclusive boundary plus a range map of completed uploads. That made the state hard to reason about, caused the seeder to restart from the last confirmed upload, and left stale completed views accumulating behind the confirmed frontier.

Validation

• cargo test -p battleware-node upload_tracker_advances_past_out_of_order_completions_once_gap_closes
• cargo test -p battleware-node test_good_links
• cargo fmt --all -- --check

Closes #6.