Item filtering refactor

[MatthewMarinets]

What task needs to be completed?

Writing down goals and design decisions following discussion with Ziktofel on 2024-09-21

Goals:

• Locked items option should behave consistently (currently can be filtered for transport hook, a PF upgrade, and zerg flyer W/A upgrades)
• Consolidate "necessary" flag with locked where appropriate
  • within PoolFilter.py "Locked", "Necessary" -> "Requested", "Locked"
• Split "excluded" flag depending on how important it is to respect
• PoolFilter.py (item culling) should use the same flag system as init.py (item filtering)
  • Maybe move item filtering to its own file to keep init.py smaller
• Add an allow_generation_failure yaml-only option (invisible on website), which controls if the generator will try to adjust invalid option arrangements to make a valid world, or will fail with an error message if the world is invalid.
• General cleanup -- remove unused "origin" field on ItemData

Flag changes:

• Necessary -- remove it. Consolidate with Locked or Requested where appropriate.
• Requested -- used within item culling, for an item that is requested to be locked to meet upgrade counts, but can be overridden if a parent is culled (replace weird locking behaviour for zerg flyer w/a upgrades, transport hook, and PF orbital abilities)
• Removed -- used for w/a upgrades of the wrong package type. Overrides all other options, cannot be added back in even if locked
• Culled -- used for items that are excluded by item culling, but which may be added back in even if allow_generation_failures is true.
• Excluded -- used for user excludes through options. Excluded items should be respected unless overridden with locks or if allow_generation_failures is off to meet mission logic

The filter flag priority hierarchy is:

1. removed
2. start_inventory
3. locked
4. excluded
5. requested
6. culled

*Note requested and culled should generally be mutually exclusive, so their hierarchy can be changed to make the implementation easier.

[Ziktofel]

See #333 (comment)