Add merkle tree as example

[rkdud007]

https://github.com/rkdud007/sp1-merkle-tree This prgram gets element numbers as input, insert incrementally to keccak Merkle Tree, then generate the proof and verify all the elements.

Speed

note: this is not from proper benchmark.

count: 16
Proof generation time: 4.571703375s

count: 32
Proof generation time: 12.891774042s

count: 64
Proof generation time: 28.686333084s

count: 128
Proof generation time: 54.064973208s

note

rely merkle-tree implementation on https://github.com/rkdud007/alloy-merkle-tree/tree/sp1-support