Export 'fakeDataStore' for reuse in downstream tests

[MregXN]

What would you like to be added:
In upstream, there is an internal fakeDataStore that is used for testing but is currently not exported.
(e.g.,

gateway-api-inference-extension/pkg/epp/datalayer/metrics/logger_test.go

Line 97 in 497f376

type fakeDataStore struct{}

)

In some downstream use cases, we have found it useful to rely on a fake datastore with the same behavior. Since the upstream implementation is not accessible, similar fake implementations need to be duplicated in downstream test code (for example, llm-d/llm-d-inference-scheduler#24).

Why is this needed:

• Reducing duplicated test-only implementations downstream
• Keeping test behavior aligned with upstream
• Lowering long-term maintenance overhead for both sides

[danehans]

@MregXN are you able to work on this issue?

[MregXN]

@MregXN are you able to work on this issue?

I can take it. Feel free to assign to me please.