[Python] Add clear method for builder reuse #5817

Job	Run time
Build Linux (g++-13)	39s
Build Linux (clang++-15)	40s
Build Linux C++ (11, g++-13)	36s
Build .NET Windows	1m 33s
Build Windows C++ (11)	3m 15s
Build .NET Windows (-p:UnsafeByteBuffer=true)	1m 34s
Build Linux with -DFLATBUFFERS_NO_FILE_TESTS	40s
Build Windows C++ (14)	3m 10s
Build Windows C++ (17)	3m 42s
Build Windows C++ (20)	5m 53s
Build Linux with out-of-source build location	30s
Build Linux C++ (11, clang++-15)	39s
Build Mac (for Intel)	3m 2s
Build Windows C++ (23)	5m 3s
Build Linux C++ (14, g++-13)	32s
Build Linux C++ (14, clang++-15)	37s
Build Windows 2019	3m 48s
Build Linux C++ (17, g++-13)	38s
Build Windows 2017	4m 6s
Build Windows 2015	3m 28s
Build Linux C++ (17, clang++-15)	38s
Build Linux C++ (20, g++-13)	55s
Build Android (on Linux)	2m 59s
Build Linux C++ (20, clang++-15)	39s
Build Benchmarks (on Linux) (g++-13)	1m 5s
Build Linux C++ (23, g++-13)	38s
Check Generated Code (g++-13)	31s
Check Generated Code (clang++-15)	27s
Check Generated Code on Windows	3m 34s
Build Go	1m 2s
Build Java	20s
Build Kotlin Linux	1m 51s
Build Kotlin MacOS	7m 41s
Build Mac (universal build)	6m 53s
Build PHP	22s
Build Python	29s
Build Rust Linux	1m 12s
Build Rust Windows	1m 17s
Build Swift	1m 20s
Build Dart	35s
Build Nim	30s
Build Swift Wasm	1m 6s
Build TS	44s
release-digests	0s
provenance	0s
	1h 20m 53s

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