Feature/init with root

[StanChe]

Initializing a tree with a root

This PR modifies the account-compression program allowing the creation of the trees that were prepared offline. It allows creating trees with or without a canopy.
Verification of the validity, events, any additional checks and fields (URLs, hashes, etc.), and any additional permissions for the created tree are left to the discretion of the calling program.

The workflow

sequenceDiagram
autonumber
actor TC as Tree creator program
participant AC as account-compression
activate TC
TC ->> AC: prepare_tree(tree_account, max_depth, max_buffer_size)
AC -> AC: initializes the header, but not the tree
loop For a tree with a canopy
TC ->> AC: append_canopy_nodes(tree_account, start_index, canopy_nodes)
end
TC ->> AC: finalize_merkle_tree_with_root(tree_account, root, rightmost_leaf, rightmost_index, proof)
AC -> AC: verifies the canopy is valid
AC -> AC: initializes the tree

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This change is inspired by solana-labs#6441

Next steps

The current master is giving similar errors when building the contract:

...
 Compiling spl-account-compression v0.3.0 (xxx/solana-program-library/account-compression/programs/account-compression)
Error: Function _ZN23spl_account_compression23spl_account_compression30finalize_merkle_tree_with_root17h9805555f38fa9781E Stack offset of 4976 exceeded max offset of 4096 by 880 bytes, please minimize large stack variables
Error: Function _ZN23spl_account_compression23spl_account_compression12replace_leaf17h2b3444654638b071E Stack offset of 4976 exceeded max offset of 4096 by 880 bytes, please minimize large stack variables
Error: Function _ZN23spl_account_compression23spl_account_compression11verify_leaf17ha925f198f492934cE Stack offset of 4912 exceeded max offset of 4096 by 816 bytes, please minimize large stack variables
Error: Function _ZN23spl_account_compression23spl_account_compression16insert_or_append17hc0d69cec9d07924fE Stack offset of 4952 exceeded max offset of 4096 by 856 bytes, please minimize large stack variables
    Finished release [optimized] target(s) in 30.04s
...

This PR does not change that. It appears to be related to the anchor - solana sdk versions on master. All the existing and the new tests are working fine though, but whether this might create some issues during deploys is unknown.

As a separate note empty_node_cached in the concurent merkle tree library was used as if it was modifying the passed in cache, but in fact it was not, this PR adds empty_node_cached_mut that caches the already processed nodes, but it doesn't change the existing logic.