Same aggregation circuit, verifies different snarks with different vkeys
(same standard plonk gate, but different selectors / copy constraints)

* fix: save break points when generating agg circuit for first time

* chore: add circuit files to gitignore

* feat: halo2-lib universal verifier example

* chore: cargo fix

`omega` which changes when `k` changes, so all shift computations need
to be done as witness. Current implementation is likely not the most
optimal. Instead of storing `shift` as `omega^i`, we store just
`Rotation(i)`. We de-duplicate when possible using `BTreeMap` of
`Rotation`. Note you must use `Rotation` instead of `F` for `BTreeMap`
because the ordering of `omega^i` may change depending on `omega`.

This reverts commit 69f648e.

Add example using halo2-lib for range check where lookup table size
changes depending on `k`.