Allow writing Variant to files and test parquet-variant IO #30219

Job	Run time
Rust (docs)	2m 50s
lint-toml	7s
Rust build (wasm32 with default features)	54s
Python (lint)	42s
License Check and Audit Check (bans licenses sources)	52s
Check generated source files are up to date	42s
validate-workflow-yaml	6s
Public API lock files	1m 2s
Rust (lint)	2m 36s
Rust tests (linux-arm64)	4m 57s
Python (test)	2m 26s
C++ build	1m 32s
C/C++ (lint)	6s
Java	2m 15s
Rust build (default features)	2m 14s
SQL logic tests	2m 17s
Rust tests (windows-x64)	8m 30s
Rust (lint, no default)	1m 45s
Rust build (with tokio dispatcher)	1m 7s
Rust build (all-features)	2m 11s
Check build with minimal dependencies	1m 31s
License Check and Audit Check (advisories)	51s
C API test build	35s
WASM integration smoke test	1m 59s
	44m 7s

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