Generation failsafes: automatic location/mission exclusions to respect item exclusion

[MatthewMarinets]

What task needs to be completed?

Writing down results of discussion with Ziktofel 2024-09-21

Currently, if a player has invalid options in the sense of excluding too many items for their mission load, there are some issues:

• Items get locked or start-inventoried, potentially ignoring other user settings
• Messages about what's going on are poor
• If there were messages, they wouldn't be visible when generating from website

Suggested changes:

• Add an allow_generation_failure yaml-only flag (see Item filtering refactor #309)
• For a logic failsafe, exclude missions and locations instead of adding items, as it's less noticeable / more in-line with user expectations
• Before placing missions, check which victory/challenge/mastery/vanilla locations are possible with item exclusions
  • If a mission is not excluded but a victory location is unreachable, exclude the mission
  • If a mission is not excluded and a non-victory location is unreachable and that location is not excluded, exclude the location
• Emit a message saying exactly what was excluded. Bonus: include counts for how many missions and locations were excluded
• If allow_failures is on, fail the generation

Note vanilla exclusions are rarely necessary in cases like Last Stand 1.5 Billion Zerg. It may be worthwhile to flag them separately in the location data for faster checking.