Refactor `convert` command #2430

Job	Run time
check	31s
test x86_64-unknown-linux-gnu - stable	1m 49s
deny (bans licenses sources)	33s
test x86_64-unknown-linux-gnu - beta	1m 54s
test x86_64-unknown-linux-gnu - nightly	1m 4s
deny (advisories)	33s
fuzz pica-record-ref	3m 30s
test x86_64-apple-darwin - stable	1m 49s
cross x86_64-unknown-linux-musl - stable	47s
fuzz pica-record-matcher	3m 33s
test x86_64-pc-windows-gnu - stable	3m 43s
cross aarch64-unknown-linux-gnu - stable	44s
fuzz pica-path	3m 30s
test i686-pc-windows-msvc - stable	3m 45s
cross aarch64-unknown-linux-musl - stable	47s
fuzz pica-format	3m 31s
fuzz pica-query	3m 33s
miri ${{ matrix.item.name }}	0s
careful	0s
fmt	0s
clippy	0s
msrv	0s
audit	0s
docs	0s
udeps	0s
ci	0s
	35m 36s

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