feat(rules): add rules.Store and in-memory implementation

[jpower432]

Description

Creates a way to index and interact with rule set extension data gather from OSCAL Components. Starts with a basic in-memory implementation using maps for efficient searching.

Closes #8

Decisions

These might need feedback

Making the Store interface: It's very likely that other implementations will be needed to scale to larger datasets or to support for concurrent searches. Creating an interface that can be used will allow these implementation to be used easily.
Adding context to the Store Interface - Essentially future proofing the interface. Added so that the interface does not need to be broken or rewritten if implementation include the use of remote calls. This is a medium opinion though and I could probably go either way on including this.

How has this been tested?

• Unit tests added with testdata based testdata from C2P
• Using in a C2P prototype implementation

Types of changes

• New feature (non-breaking change which adds functionality)

Quality assurance (all should be covered).

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing tests pass locally with my changes
• All commits are signed-off.

[jpower432]

@yana1205 Just wanted to add some context, the in-memory implementation should overlap with the functionality of the OSCAL parser in C2P Go, but this implementation does not have the control context.

[yana1205]

Added so that the interface does not need to be broken or rewritten if implementation include the use of remote calls.

If there is a possibility of storing OSCAL objects in external storage in the future, adding context.Context to the interface now is reasonable.
While it's technically possible to embed context.Context in a "struct" that implements the interface without passing through argument, it affects the entire struct's lifecycle, making it less flexible for handling multiple concurrent requests with different contexts.