Merge rust-bitcoin/rust-bitcoin#3724: units: Seal the `Integer` trait #94

Job	Run time
Prepare	3s
Test - stable toolchain (minimal)	17m 47s
Docs - stable toolchain (recent)	57s
Test - stable toolchain (recent)	18m 41s
Test - MSRV toolchain (minimal)	28m 25s
Test - MSRV toolchain (recent)	28m 4s
Test 32-bit version	48s
Cross test - stable toolchain	1m 44s
Kani codegen - stable toolchain	55s
WASM - stable toolchain	1m 32s
ASAN - nightly toolchain (recent)	40s
Docs - nightly toolchain (recent)	1m 8s
API - nightly toolchain (recent)	1m 32s
Bench - nightly toolchain (recent)	1m 45s
Embedded - nightly toolchain	1m 17s
Lint - nightly toolchain (recent)	58s
Test - nightly toolchain (minimal)	14m 59s
Test - nightly toolchain (recent)	15m 59s
	2h 17m 14s

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