flatbuffer builder reuse #4720

Job	Run time
ci (ubuntu-20.04, 18, Release)	6m 26s
ci (ubuntu-20.04, 18, Debug)	5m 36s
ci (ubuntu-22.04, 20, Release)	5m 42s
ci (ubuntu-22.04, 20, Debug)	5m 17s
ci (ubuntu-24.04, 20, -Db_sanitize=address, Release)	8m 36s
ci (ubuntu-24.04, 20, -Db_sanitize=address, Debug)	5m 57s
ci (ubuntu-24.04, 20, -Db_sanitize=undefined, Release)	9m 8s
ci (ubuntu-24.04, 20, -Db_sanitize=undefined, Debug)	6m 30s
ci (ubuntu-24.04, 20, -Db_sanitize=thread, Release)	7m 18s
ci (ubuntu-24.04, 20, -Db_sanitize=thread, Debug)	5m 51s
ci (macos-12, 18, Release)	10m 58s
ci (macos-12, 18, Debug)	7m 35s
ci (macos-14, 20, Release)	4m 43s
ci (macos-14, 20, Debug)	4m 51s
ci (windows-2022, 20, Release)	8m 51s
ci (windows-2022, 20, Debug)	8m 28s
	1h 51m 47s

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