Merge ElementsProject/rust-elements#289: Improve types on `AssetIssua… #801

Job	Run time
Lint - nightly toolchain	1m 31s
Test - msrv toolchain (recent)	1m 28s
Docs - nightly toolchain	1m 19s
Check WASM	38s
Docs - stable toolchain	1m 23s
Bench - nightly toolchain	1m 41s
Test 32-bit version	59s
Test - stable toolchain (recent)	5m 59s
Test - nightly toolchain (recent)	6m 11s
Cross test	1m 37s
	22m 46s

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