Introduce ManyToMany and OneToOneThrough builder

[solnic]

This adds support for building associated structs in case of ManyToMany and OneToOneThrough association types, where intermediate join tables are involved. It works with persistable and in-memory structs.

factories.define(:user) do |f|
  f.first_name { fake(:name, :first_name) }
  f.last_name { fake(:name, :last_name) }
  f.email { fake(:internet, :email) }
  f.timestamps

  f.association :address
end

factories.define(:user_address) do |f|
  f.association(:user)
  f.association(:address)
  f.timestamps
end

factories.define(:address) do |f|
  f.full_address { fake(:address, :full_address) }
end

# Persisted struct
factories[:user]
# #<ROM::Struct::User id=2 last_name="Leuschke" first_name="Don" alias=nil email="[email protected]" created_at=2023-11-24 10:19:25.693242 +0000 updated_at=2023-11-24 10:19:25.693246 +0000 age=nil type=nil address=#<ROM::Struct::Address id=2 full_address="44090 Patrina Vista, Barrowsburgh, SC 87402" user_id=2>>

# In-memory struct works too
factories.structs[:user]
#<ROM::Struct::User id=1 last_name="Zieme" first_name="Mallory" alias=nil email="[email protected]" created_at=2023-11-24 10:20:05.920642677 +0000 updated_at=2023-11-24 10:20:05.920648427 +0000 age=nil type=nil address=#<ROM::Struct::Address id=1 full_address="Suite 376 7225 Ortiz Centers, East Desmondland, MT 16834-2493" user_id=1>>

[solnic]

Switching to Draft again as there are a couple of issues to address