Less repeatedly spawning item groups when checking consistency

[SurFlurer]

Summary

Performance "Less repeatedly spawning item groups when checking consistency"

Purpose of change

Fix #71371

I noticed that the flame graph of item_group::check_consistency can be divided into two blocks that are similar in shapes. That makes me guess that some groups are spawned multiple times. In fact there's too much unnecessary spawning. We actually do not need to spawn everything over and over if there's no container to restrain them.

Describe the solution

Introduce a bool parameter actually_spawn to the callstack of check_consistency(). The logic below stands on the point that spawning is different from checking consistency. Every item groups and single item creators get their consistency checked, so there's unlikely to be omissions.

1. When checking an item group, if it doesn't define a container, we do not need to spawn it as a whole, just get individual entries spawned is enough.
2. When checking a single item creator, if it points to an item group and doesn't define a container, we do not need to spawn it, because the item group will be spawned separately.

Describe alternatives you've considered

collection type item groups automatically spawn all entries when checking consistency, so unless the item group's type is distribution, there's no need to spawn all entries individually. ( this is what the first commit does )

Gains from this alternative:

Not as seductive as the the main solution, but I think it's less likely to introduce problems.

Testing

It reduces the time spent on verifying items from 12ish seconds to 2ish seconds.

before:

( note the item_group::check_consistency line )

after:

I also randomly fiddled with some itemgroups to ensures that their errors can still be detected by new code.

Additional context

[Inglonias]

Bravo! Good job.