pem-rfc7468: add `detect_base64_line_width` and `new_detect_wrap` (#1… #1882

Job	Run time
build (1.65.0, thumbv7em-none-eabi)	2m 2s
build (1.65.0, wasm32-unknown-unknown)	2m 8s
build (stable, thumbv7em-none-eabi)	15s
build (stable, wasm32-unknown-unknown)	17s
test (1.65.0)	2m 9s
test (stable)	19s
minimal-versions / minimal-versions	29s
	7m 39s

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