Fix AvroReader: Add union resolving for nested struct arrays #32899

Job	Run time
build with wasm-pack	2m 31s
cargo test (win64)	57m 38s
cargo check	6m 36s
Check cargo fmt	39s
cargo test (macos)	9m 56s
cargo test (macos-aarch64)	10m 31s
Verify MSRV (Min Supported Rust Version)	6m 54s
Verify Vendored Code	52s
cargo examples (amd64)	12m 46s
cargo test (amd64)	10m 6s
cargo test datafusion-cli (amd64)	4m 5s
cargo doc	4m 0s
cargo test doc (amd64)	15m 36s
Run sqllogictest with Postgres runner	3m 35s
check Cargo.toml formatting	2m 53s
clippy	5m 55s
check configs.md is up-to-date	3m 5s
cargo test hash collisions (amd64)	14m 54s
cargo test pyarrow (amd64)	31s
verify benchmark results (amd64)	12m 52s
	3h 5m 55s

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