Add incrementScore to RedisZSet

[vinsguru]

Adds a method to increment the score of an element in a Redis sorted set.
Implements the Redis ZINCRBY command through Spring Data’s RedisZSet.
Includes a test verifying score updates for existing and new members.

Closes #3256

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[onobc]

Thank you for the contribution @vinsguru ! Nice work.

Closing via onobc@1e904a1