BP-25: MovingChecksumToProto--Refactor the checksum part of bookkeeper

Motivation​

Current the checksum implementation is in client module while the checksum semantic is more close to protocol. Moreover, moving the checksum implementation to protocol will avoid server module's dependency to client module when doing checksum in server side.

Public Interfaces​

An internal refactor not affecting public interfaces.

Proposed Changes​

Move the DigestManager and related classes to proto module

Compatibility, Deprecation, and Migration Plan​

N/A

Test Plan​

The original all tests should work as before.

Rejected Alternatives​

N/A