benchmarks: add ad hoc benchmark for 'quick-strings' #1877

Job	Run time
msrv	1m 58s
miri	9m 5s
build-for-x86-64-but-non-sse-target	35s
rebar	2m 32s
rustfmt	14s
wasm	1m 17s
test (stable, ubuntu-latest, stable)	2m 55s
wasm-no-simd128	51s
test (beta, ubuntu-latest, beta)	2m 0s
test (nightly, ubuntu-latest, nightly)	1m 58s
test (macos, macos-latest, stable)	1m 19s
test (win-msvc, windows-latest, stable)	3m 15s
test (win-gnu, windows-latest, stable-x86_64-gnu)	3m 16s
test (stable-x86, ubuntu-latest, stable, i686-unknown-linux-gnu)	1m 47s
test (stable-aarch64, ubuntu-latest, stable, aarch64-unknown-linux-gnu)	2m 3s
test (stable-powerpc64, ubuntu-latest, stable, powerpc64-unknown-linux-gnu)	1m 57s
test (stable-s390x, ubuntu-latest, stable, s390x-unknown-linux-gnu)	1m 52s
	38m 54s

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