perf(turbopack): Use `Arc<String>` instead of `String` #7511

Job	Run time
Determine jobs to run	18s
Turbopack rust check	51s
Benchmark and compare Turbopack performance on ${{ matrix.os.title }}	0s
Benchmark on ${{ matrix.bench.name }}	0s
Done	3s
Store benchmark result	0s
Cleanup / cleanup	4s
	1m 16s

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