Foreign fields 4: Multiplication

[mitschabaude]

• add 3 different gadgets that use the ffmul gate: ForeignField.mul(), ForeignField.inv(), ForeignField.div()
  • gadget design closely follows https://github.com/o1-labs/rfcs/blob/main/0006-ffmul-revised.md
• add foreign field unit tests with numbers not reduced modulo f, where applicable
• change the return signature of ZkProgram.analyzeMethods() to be nicer to read and to match SmartContract.analyzeMethods() (seems kinda unrelated; I did this to inspect number of rows of some ffmul methods. It's technically a breaking change but low impact)

bindings: o1-labs/o1js-bindings#206

closes #1142

[Trivo25]

this is awesome! Really appreciate all the descriptive comments

[querolita]

Excellent job! I would nonetheless like to clarify a question about the circuit shape before accepting, to make sure all checks are getting in. I also have a question regarding division 💯

[jspada]

Approved with minor suggestions and a question.