Add more evaluator examples to `dokimos-examples` module

[fkapsahili]

The length-based evaluator from the original ask now exists as ResponseLengthEvaluator in the Spring AI tutorial example. What's still missing is an example for semantic similarity / deduplication of retrieved context chunks, so this issue now tracks just that.

[fkapsahili]

The length-based evaluator from this is already covered by ResponseLengthEvaluator in the Spring AI tutorial example, so I've narrowed this down to the part that's still missing, the semantic similarity / context chunk dedup example.