Cardano Updates

Additional changes:
- also move the `SignableBuilder` that use digesters utilities to a
  `signable_builder` module: `CardanoDatabaseSignableBuilder` and
  `CardanoImmutableFilesFullSignableBuilder`
- add `entities` module that contains `ImmutableFile` and `LedgerStateSnapshot`
- add `test` module that contains public and private test utilities,
  such as:
  - the `DummyCardanoDbBuilder`
  - a `double` submodule with `the `DumbImmutableDigester` and the `DumbImmutableFileObserver`

* mithril-aggregator from `0.7.61` to `0.7.62`
* mithril-client from `0.12.13` to `0.12.14`
* mithril-signer from `0.2.252` to `0.2.253`
* openapi.yaml from `0.1.49` to `0.1.50`

This will make the CI fail if the `Cargo.lock` was not updated after a
change in a `Cargo.toml` such as a version bump.

- rewrite `API_VERSION_MISMATCH_WARNING_MESSAGE` value
- use tuple match instead of nested `if let` / `match` / `if` for better readability
- improve `warn!` usage
- enhance test readability

This will make the CI fail if the cargo lock was not updated after a
change in a Cargo.toml such as a version bump.

To make sure that both json hex and bytes hex encoding are supported.

Using 'bincode' crate.