Implement FFadd and FFMul in large prime fields

[mitschabaude]

Application: RSA, zk-email, zk JWTs

Note: This is similar to #1142 and #1180, but those issues will be done for foreign fields up to 259 bits. For RSA, we need much bigger fields with sizes of 2048 bits or similar.

For small fields, there are targeted FFadd and FFmul custom gates which do addition or multiplication in a single gate (1-2 rows) plus a few range checks on outputs.

However, for large fields we don't have such specific custom gates. This issue is about implementing big-field arithmetic without additional custom gates, only using available primitives.

Primitives that could be useful:

• native addition and multiplication Field.add, Field.mul
• Gadgets.rangeCheck64 already exposed in o1js
• 3x88-bit range check that will be exposed as part of Port FFMUL gadget to TypeScript #1142 or Port FFadd and FFsub gadget to TypeScript #1180
• Bigint addition on 3 x 88-bit limbs that'll be exposed as part of Port FFMUL gadget to TypeScript #1142
• Possibly the ffmul gadget that'll be exposed as part of Port FFadd and FFsub gadget to TypeScript #1180