fix: Add warning if relying on Redis max_connections parameter

[keelerm84]

The new_feature_store and new_big_segment_store methods accept a
max_connections parameter that has been unused since v8.

We cannot start using this parameter now as it would be a functionally
breaking change. Instead, we are opting to warn customers who might try
setting it explicitly.

fixes #386

---

Note

Warns when non-default max_connections is passed to Redis stores, documents it as unused, and adds tests verifying behavior.

• Redis integrations:
  • Add warning in Redis.new_feature_store and Redis.new_big_segment_store when max_connections differs from Redis.DEFAULT_MAX_CONNECTIONS; advise using redis_opts={'max_connections': N}.
  • Update docstrings to mark max_connections as deprecated/unused.
  • Import ldclient.log to emit warnings.
• Tests (ldclient/testing/integrations/test_redis.py):
  • Verify max_connections arg does not affect Redis connection pool for feature store and big segment store.
  • Verify warnings are logged when max_connections is non-default and not when default.

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