md5: add LoongArch64 CI job, minor code tweaks, bump to v0.10.6 #966

Job	Run time
test-msrv	5m 13s
minimal-versions / minimal-versions	2m 50s
set-msrv / set-msrv	6s
test (1.57.0)	7m 16s
build (1.57.0, thumbv7em-none-eabi)	3m 20s
test (stable)	2m 58s
cross (1.57.0, aarch64-unknown-linux-gnu, default)	5m 4s
build (1.57.0, wasm32-unknown-unknown)	3m 24s
cross (1.57.0, powerpc-unknown-linux-gnu, default)	6m 13s
build (stable, thumbv7em-none-eabi)	24s
build (stable, wasm32-unknown-unknown)	35s
cross (stable, aarch64-unknown-linux-gnu, default)	1m 50s
cross (stable, powerpc-unknown-linux-gnu, default)	1m 44s
	40m 57s

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