feat(commands): ZINTER, ZINTERSTORE, ZUNION, ZUNIONSTORE: add a new aggregator: COUNT

[nkaradzhov]

Description

Describe your pull request here

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Checklist

• Does npm test pass with this change (including linting)?
• Is the new or changed code fully tested?
• Is a documentation update included (if this change modifies existing APIs, or introduces new ones)?

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Note

Low Risk
Small, additive API surface change (TypeScript union type widening) with extensive new tests; runtime behavior is limited to passing through an additional string to Redis on opt-in.

Overview
Adds support for Redis 8.8’s AGGREGATE COUNT option across ZINTER, ZINTERSTORE, ZINTER WITHSCORES, ZUNION, ZUNIONSTORE, and ZUNION WITHSCORES by widening the options types and reusing ZUNION’s option type in ZUNIONSTORE.

Expands the test suite with argument-parsing assertions and integration tests (gated behind minimumDockerVersion: [8, 8]) to validate COUNT behavior and to ensure existing SUM/MIN/MAX aggregations still work.

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