Add `UnionValue` and `UnionScalar` #33878

Job	Run time
lint-toml	7s
Python (test)	3m 30s
C++ API	2m 1s
License Check and Audit Check (bans licenses sources)	53s
Rust build (with tokio dispatcher)	2m 37s
Rust build (wasm32 with default features)	8m 34s
Rust build (default features)	8m 2s
validate-workflow-yaml	7s
WASM integration smoke test	2m 27s
Rust build (all-features)	8m 2s
Python CUDA (test)	4m 20s
Python (lint)	1m 57s
measurement_id golden vectors	15s
Check build with minimal dependencies	2m 13s
Check generated source files are up to date	58s
Rust (btrblocks golden corpus)	53s
C API test build	57s
Rust (lint, no default)	2m 58s
Java	2m 26s
License Check and Audit Check (advisories)	52s
C/C++ (lint)	8s
Mirror DuckDB to R2 / Resolve DuckDB version and check R2	6s
Mirror DuckDB to R2 / Mirror DuckDB ${{ matrix.archive }} to R2	0s
DuckDB libraries available in R2	2s
Rust (lint)	3m 30s
SQL logic tests	5m 4s
Rust tests (windows-x64)	7m 32s
Rust (docs)	5m 6s
Rust tests (linux-arm64)	5m 33s
	1h 21m 10s

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