chore: Support persistent data store verification in contract tests

[keelerm84]

BEGIN_COMMIT_OVERRIDE
chore: Support persistent data store verification in contract tests
fix: Update Redis to write missing $inited key
fix: Redis store is considered initialized when $inited key is written
END_COMMIT_OVERRIDE

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Note

Medium Risk
Touches client evaluation/initialization gating and persistent store initialization semantics, which could affect flag evaluations during startup or when relying on cached data; changes are scoped and mainly exercised via contract tests.

Overview
CI contract tests now run with persistent-store verification enabled for both v2 and v3 (bumped to v3.0.0-alpha.2).

The contract test service advertises persistent store capabilities and the Python contract-test client can now configure persistent feature stores (and v3 dataSystem stores/modes) for Redis, DynamoDB, and Consul, including cache settings.

SDK behavior is adjusted to treat cached persistent-store data as usable before full initialization, and the Redis feature store now writes/reads the $inited key during init to correctly report initialization.

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