Let `ReadableKVState` and `WriteableKVState` require Records as values

[rbair23]

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👾 Description of the issue

The are two primary interfaces for interacting with key/value data in the state (akin to a database): ReadableKVState.java and WriteableKVState.java. The former is used for reading data in a key/value state, and the latter is for updating data in a key/value state. The values read from and provided to these interfaces should always be records which are inherently immutable. When providing a new value to the WriteableKVState, another instance of the record is made with the updated values. This new record is provided to the WriteableKVState. The problem is that the interfaces do not strictly enforce this. It is possible to create implementations of ReadableKVState and WriteableKVState that do not use immutable data, which could lead to bugs.

Steps to reproduce

See the ReadableKVState.java and WriteableKVState.java interfaces. Observe that the use of records for the parameterized value V is not required to be a record.

Proposed Solution:

Update the definitions of ReadableKVState and WriteableKVState to:

public interface ReadableKVState<K, V extends Record>
public interface WritableKVState<K, V extends Record> extends ReadableKVState<K, V>

Once these changes are made, other class definitions will need the same change so they are compatible. These can be found by attempting to compile the project. In addition, there are unit tests that use String as values. While java strings are immutable, they do not extend Record so they must be updated to be compatible. This can be accomplished by creating a record wrapper:

public record StringRecord(String value) {}

and updating values used from

String APPLE = "Apple"

to

StringRecord APPLE = new StringRecord("Apple")

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