fix(js): free native strings #480

Job	Run time
Lint	1m 16s
Build Android Libraries (aarch64-linux-android)	2m 57s
Build Android Libraries (armv7-linux-androideabi)	2m 37s
Build Android Libraries (i686-linux-android)	2m 27s
Build Android Libraries (x86_64-linux-android)	2m 57s
Build Library (linux-aarch64, anoncreds-ubuntu-latest, aarch64-unknown-linux-gnu, libanoncreds.so...	5m 50s
Build Library (linux-x86_64, anoncreds-ubuntu-latest, x86_64-unknown-linux-gnu, libanoncreds.so, ...	4m 49s
Build Library (darwin-x86_64, macos-latest, x86_64-apple-darwin, libanoncreds.dylib)	6m 35s
Build Library (darwin-aarch64, macos-latest, aarch64-apple-darwin, libanoncreds.dylib)	7m 24s
Build Library (darwin-universal, macos-latest, darwin-universal, libanoncreds.dylib)	13m 42s
Build Library (windows-x86_64, anoncreds-windows-latest, windows-x86_64, x86_64-pc-windows-msvc, ...	5m 28s
Build ios Libraries (aarch64-apple-ios)	4m 55s
Build ios Libraries (aarch64-apple-ios-sim)	7m 2s
Build ios Libraries (x86_64-apple-ios)	4m 58s
Test (anoncreds-windows-latest)	6m 39s
Test (anoncreds-ubuntu-latest)	3m 54s
Create android libraries	0s
Create ios xcframework	0s
Create iOS and Android Release Assets	0s
Build and Test JavaScript wrapper	1m 39s
Build Python (anoncreds-ubuntu-latest, linux-aarch64, manylinux2014_aarch64)	15s
Build Python (anoncreds-ubuntu-latest, linux-x86_64, manylinux2014_x86_64)	35s
Build Python (macos-latest, darwin-universal, macosx_10_9_universal2)	43s
Build Python (anoncreds-windows-latest, windows-x86_64, win_amd64)	27s
	1h 27m 9s

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