Add retry of failed calls for AiClient, EmbeddingClient and VectorStore

[tzolov]

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• Refactor the EmbeddingResponse and Embedding from “class” into “record” types. Fix the affected code get calls.
• Refactor the TransformersEmbeddingClient to avoid telescopic public methods call anti-patter.
• Add spring-retry dependency to spring-ai-core.
• Implement RetryAiClient, RetryEmbeddingClient and RetryVectorStore as decorators around AiClient, EmbeddingClient and VectorStore instance. The retry decorators use RetryTemplate to wrap all delegate methods calls. Default RetryTemplate is provided with each instance.
• Add Tests for all Retry decorators.
• Add missing javadocs to existing core classes.

Resolves #123