[Cosmos] Extract a StoreResult test factory to replace the 20-arg positional constructor in unit tests

## Summary

Follow-up from PR [#48914](https://github.com/Azure/azure-sdk-for-java/pull/48914) (review feedback from @kushagraThapar).

The 20-arg positional `new StoreResult(...)` constructor is repeated across many test methods (in `ConsistencyWriterTest.java` at lines ~667, 725, 757, 779, 834, 894, 903, 919, 947, and several more in `QuorumReaderTest.java`). Each invocation follows the same pattern: most arguments are constants/`null`/`false`, with only 2–3 meaningful per test (replica role, `isThrottledException`, `isValid`).

This positional-constructor accretion has been growing across multiple PRs and makes tests verbose and fragile.

## Proposed change

Extract a `StoreResultTestFactory` (or builder) with named, intent-revealing methods, e.g.:

- `throttled429()`
- `valid(int globalCommittedLsn)`
- `unhealthy(replicaRole)`

Benefits:
- New tests become 1-line setup instead of ~20-line setup.
- When the `StoreResult` constructor changes (e.g. adding a 21st arg), only the factory updates instead of N test sites.
- Test intent becomes self-documenting (`throttled429()` reads as a behavior, not a 20-arg ctor invocation).

## Scope

Test-only refactor; no production behavior change. Update existing `StoreResult`-based tests in:
- `sdk/cosmos/azure-cosmos-tests/.../directconnectivity/ConsistencyWriterTest.java`
- `sdk/cosmos/azure-cosmos-tests/.../directconnectivity/QuorumReaderTest.java`

## Context

Reviewer noted this is "not a blocker for [PR #48914] but worth scheduling as a follow-up before the next test wave lands on top."