move usage towards AsChar method instead of functions under the chara… #1031

Job	Run time
Bench	49s
Check formatting	14s
Coverage	59s
Build documentation	55s
Test minimal rust version	20s
Test (stable)	43s
Test (beta)	44s
Test (nightly)	46s
Test (1.65.0)	50s
Test (stable, --features "std")	47s
Test (stable, --no-default-features)	36s
Test (stable, --no-default-features --features "alloc")	40s
Test (nightly, --no-default-features)	37s
Test (nightly, --no-default-features --features "alloc")	42s
	9m 42s

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