[Python] Add clear method for builder reuse #5815

Job	Run time
Build Linux with out-of-source build location	39s
Build Windows C++ (11)	3m 47s
Build Windows C++ (14)	3m 27s
Build Benchmarks (on Linux) (g++-13)	1m 37s
Build Android (on Linux)	2m 19s
Build Windows C++ (17)	3m 36s
Build Windows C++ (20)	4m 58s
Build Windows C++ (23)	5m 0s
Build Dart	43s
Build .NET Windows	59s
Check Generated Code (g++-13)	41s
Build .NET Windows (-p:UnsafeByteBuffer=true)	31s
Check Generated Code on Windows	3m 35s
Check Generated Code (clang++-15)	30s
Build Go	50s
Build Java	20s
Build Kotlin Linux	2m 12s
Build Kotlin MacOS	3m 24s
Build Linux (g++-13)	37s
Build Linux (clang++-15)	43s
Build Linux C++ (11, g++-13)	55s
Build Linux with -DFLATBUFFERS_NO_FILE_TESTS	30s
Build Linux C++ (11, clang++-15)	26s
Build Linux C++ (14, g++-13)	1m 38s
Build Mac (for Intel)	3m 24s
Build Mac (universal build)	6m 18s
Build Nim	36s
Build Linux C++ (14, clang++-15)	28s
Build Linux C++ (17, g++-13)	35s
Build PHP	22s
Build Python	16s
Build Linux C++ (17, clang++-15)	39s
Build Rust Linux	1m 11s
Build Linux C++ (20, g++-13)	30s
Build Rust Windows	1m 3s
Build Swift	1m 13s
Build Linux C++ (20, clang++-15)	30s
Build Swift Wasm	1m 4s
Build Linux C++ (23, g++-13)	32s
Build TS	42s
Build Windows 2019	4m 42s
Build Windows 2015	3m 38s
Build Windows 2017	3m 44s
release-digests	0s
provenance	0s
	1h 15m 24s

Provide feedback