KIP-683 — Add recursive support to Connect Cast and ReplaceField transforms, and support for casting complex types to either a native or JSON string

Discussion Connect

KIP-683 extends the Kafka Connect `Cast` and `ReplaceField` SMTs to support recursive field traversal into nested `Struct`, `Map`, and `Array` fields, and adds an option to cast complex-type fields to their JSON string representation. Previously these transforms operated only on top-level flat fields, making it impossible to transform or project nested schema structures common in real-world message formats without writing custom SMTs.

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