Use a shared Redis span-name attributes getter

Is your feature request related to a problem? Please describe.

Several Redis instrumentations subclass their database attributes getter only to exclude db.namespace from span names. This requires otherwise final getters to support inheritance and duplicates the workaround across Lettuce, Jedis, and Vert.x Redis.

Describe the solution you'd like

Add an internal RedisSpanNameDbAttributesGetter that delegates the attributes needed for span naming while omitting db.namespace, then use it across the affected modules.

Describe alternatives you've considered

Keep the existing anonymous subclasses in each module.

Additional context

Follow-up to #19706 and review discussion.

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