[Python] Add clear method for builder reuse #5821

Job	Run time
Build Linux with -DFLATBUFFERS_NO_FILE_TESTS	27s
Build Android (on Linux)	2m 7s
Build Benchmarks (on Linux) (g++-13)	1m 30s
Build Windows C++ (11)	3m 28s
Build Dart	38s
Build Windows C++ (14)	4m 5s
Build .NET Windows	23s
Build Windows C++ (17)	4m 26s
Build .NET Windows (-p:UnsafeByteBuffer=true)	23s
Check Generated Code (g++-13)	25s
Build Windows C++ (20)	5m 37s
Check Generated Code (clang++-15)	29s
Build Windows C++ (23)	5m 30s
Check Generated Code on Windows	4m 34s
Build Go	47s
Build Java	18s
Build Kotlin Linux	1m 33s
Build Kotlin MacOS	4m 32s
Build Linux (g++-13)	28s
Build Linux C++ (11, g++-13)	34s
Build Linux (clang++-15)	27s
Build Linux with out-of-source build location	11s
Build Linux C++ (11, clang++-15)	26s
Build Mac (for Intel)	3m 2s
Build Linux C++ (14, g++-13)	29s
Build Mac (universal build)	3m 21s
Build Nim	24s
Build Linux C++ (14, clang++-15)	30s
Build Linux C++ (17, g++-13)	27s
Build Python	18s
Build Linux C++ (17, clang++-15)	27s
Build PHP	17s
Build Linux C++ (20, g++-13)	33s
Build Rust Linux	1m 0s
Build Linux C++ (20, clang++-15)	29s
Build Rust Windows	1m 18s
Build Linux C++ (23, g++-13)	29s
Build Swift	58s
Build Swift Wasm	1m 7s
Build TS	43s
Build Windows 2019	4m 30s
Build Windows 2015	3m 55s
Build Windows 2017	4m 6s
release-digests	0s
provenance	0s
	1h 11m 41s

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