Fill: Fix remaining_fill + move_unplaceable_to_start_inventory

[Exempt-Medic]

What is this fixing or adding?

last_batch was completely unused, and fill tried to place unplaceable items, again. Now it actually uses the filler items instead and clears out unplaced_items so that they aren't reported as item/location inequality miscounts.

How was this tested?

Two-player generations with a lot of filler in local_items.

[qwint]

from a code review perspective the changes make sense to what the surrounding code is attempting to do and are minimal
tested in action with the following lingo yaml(s) and on seed 96057042239188917743 (and others but wanted to prove it wasn't a randomness fluke), it crashes gen without this change and generates fine with,

name: Player{number}
game: Lingo
Lingo:
  trap_percentage: 100
  trap_weights:
    Atbash Trap: 1
  non_local_items:
    [Atbash Trap]
---
name: Player{number}
game: Lingo
Lingo:
  trap_percentage: 100
  trap_weights:
    Atbash Trap: 1
  non_local_items:
    [Atbash Trap]