Reduce number of recursion circuits

[sai-deng]

We could potentially reuse the same recursion circuit for a small range (the number of Merkle cap bits) of proofs with different degree bits, as discussed with @Nashtare and @hratoanina.

We need to modify the Plonky2 recursive verifier to support it, which includes final polynomial evaluation of different polynomial degrees and Merkle proof verification with different Merkle path sizes.