`cairo-lang-macro` fix null-byte panics #7393

Job	Run time
build test linux x86-64	4m 15s
doc tests	3m 10s
build test windows x86-64	15m 45s
check-rust	1m 47s
check-website	10s
scarb-metadata compatibility check	48s
test linux x86-64 1/8	15m 44s
test linux x86-64 2/8	17m 17s
test linux x86-64 3/8	15m 17s
test linux x86-64 4/8	12m 45s
test linux x86-64 5/8	12m 32s
test linux x86-64 6/8	9m 21s
test linux x86-64 7/8	9m 24s
test linux x86-64 8/8	10m 28s
test windows x86-64 1/8	13m 45s
test windows x86-64 2/8	17m 2s
test windows x86-64 3/8	13m 24s
test windows x86-64 4/8	13m 19s
test windows x86-64 5/8	11m 9s
test windows x86-64 6/8	9m 26s
test windows x86-64 7/8	8m 46s
test windows x86-64 8/8	9m 49s
	3h 45m 23s

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