Reorganize merkle cryptography

[swirlds-automation]

We shouldn't have a separate cryptography instance that has merkle cryptography methods. We should just have static methods that take a regular cryptography instance.

For the thread pool, we should expose the cryptography thread pool and use it. We don't need a different thread pool for merkle cryptography and for other types of cryptography.

[swirlds-automation]

_{migrated from: url=https://github.com/swirlds/swirlds-platform/issues/6121 author:cody-littley, #:6121, createdAt:2022-10-06T15:10:29Z, updatedAt=2023-02-17T22:28:57Z labels=Backlog,Tech Debt Reduced,Migration:Base}