feat(encoding): encode usize and isize #978

Job	Run time
Test Suite	1m 53s
Check	1m 40s
Clippy	1m 17s
Rustfmt	13s
Cross compile (powerpc64-unknown-linux-gnu)	18s
Check rustdoc intra-doc links	27s
Cross compile (powerpc-unknown-linux-gnu)	27s
Cross compile (wasm32-unknown-unknown)	17s
Cross compile (armv7-unknown-linux-gnueabihf)	19s
	6m 51s

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