What

Refactoring the Dsn node for threshold encryption as a workspace with multiple crates

Why

For DX purposes. Having multiple crates allows having a better structure of code, and it makes it easier to define and run e2e-tests.

-By defining the workspace and the crates in the main Cargo.toml file.

By having the binary isolated to a single crate.
By moving all the application logic to a separate crate.
In the future the RPC server and RPC helpers will also be moved to a separate crate

cargo build

Document the interface of any function added or modified (see the coding guidelines)
Document any change to the user interface, including configuration parameters (see node configuration)
Provide automatic testing (see the testing guide).
For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, CHANGES.rst at the root of the repository for everything else).
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