AggLayer: implement `verify_leaf`

[mmagician]

To continue speccing the procedures for claim verification, we have verify_leaf_bridge that calls verify_leaf.
Its procedure signature should be as follows:

const PROOF_DATA_PTR = 0
const SMT_PROOF_LOCAL_EXIT_ROOT_PTR = 0 # local SMT proof is first
const GLOBAL_INDEX_PTR = PROOF_DATA_PTR + 2 * 256 # 512
const EXIT_ROOTS_PTR = GLOBAL_INDEX_PTR + 8 # 520
const MAINNET_EXIT_ROOT_PTR = GLOBAL_INDEX_PTR # it's the first exit root

# Operand stack: [PROOF_DATA_KEY, LEAF_VALUE[8]]
proc verify_leaf

    # 0. Load everything from the advice map into memory

    # 1. Compute GER from mainnet + rollup exit roots that are in the advice map (under PROOF_DATA_KEY)
    push.EXIT_ROOTS_PTR
    # => [exit_roots_ptr, LEAF_VALUE[8]]
    exec.crypto_utils::compute_ger
    # => [GER[8], LEAF_VALUE[8]]

    # 2. Assert the GER is valid
    exec.assert_valid_ger
    # => []

    # 3. Inspect `globalIndex` to see if we're dealing with a deposit from mainnet or from a rollup
    # probably use mem_stream to get the two words comprising global index:
    # => [GLOBAL_INDEX[8], LEAF_VALUE[8]]
    # For v0.1, let's only implement the mainnet branch:
    # => bit manipulation to assert mainnet, and to get leaf_index (it's a single Felt)
    # => [leaf_index]

    # the merkle proof and root are in memory, lets pass the right pointers to the verify_merkle_proof helper procedure
    push.SMT_PROOF_LOCAL_EXIT_ROOT_PTR
    push.MAINNET_EXIT_ROOT_PTR

    # internally, call the equivalent of `verifyMerkleProof(leafValue, smtProofLocalExitRoot, leafIndex, mainnetExitRoot)
    # Once we start implementing verify_merkle_proof, see if we should rearrange the stack?
    # => [mainnet_exit_root_ptr, smt_proof_local_exit_root_ptr, leaf_index, LEAF_VALUE[8]]
    movdn.10
    # => [smt_proof_local_exit_root_ptr, leaf_index, LEAF_VALUE[8], mainnet_exit_root_ptr]
    exec.crypto_utils::verify_merkle_proof
end

For 1., we can replicate calculateGlobalExitRoot which just applies a keccak hash to the two exit root values.

For 2. we check whether the bridge contract has this GER saved in storage. Currently the bridge only holds a single GER, soon an array.

[mmagician]

closed by #2288 & #2295