feat(observability): add redaction support for embedding span attributes

[coderabbitai]

Summary

Currently, the embeddings tracing span emits full embedding vectors and serialized response payloads as span attributes (e.g., output.value, embedding.embeddings.{index}.embedding.vector). While this conforms to the OpenInference/OpenTelemetry specification, it can result in very large span payloads for high-dimension or batched embeddings, risking dropped traces and high telemetry overhead.

Redaction support should be added to allow users to optionally suppress or truncate these large attributes (e.g., replace full vectors with compact metadata such as count and dimension).

Context

• Introduced in: feat(observability): trace span for embeddings api #84
• Comment: feat(observability): trace span for embeddings api #84 (comment)

Acceptance Criteria

• Provide a redaction/filtering mechanism for span attributes that contain large payloads (e.g., output.value, embedding.embeddings.{index}.embedding.vector)
• Ensure the default behavior still conforms to the specification
• Allow users/operators to opt in to compact metadata output (e.g., counts/dimensions only)

/cc @bzp2010