Use CPUNet-modified bech32 library #14

Job	Run time
Cross test - stable toolchain	1m 24s
Test - MSRV toolchain (recent)	6m 40s
Kani codegen - stable toolchain	59s
Test - stable toolchain (minimal)	12s
Test - stable toolchain (recent)	8s
Prepare	6s
Test - MSRV toolchain (minimal)	6m 43s
Docs - stable toolchain (recent)	12s
Test 32-bit version	48s
WASM - stable toolchain	1m 32s
Test - nightly toolchain (recent)	16s
Test - nightly toolchain (minimal)	16s
ASAN - nightly toolchain (recent)	40s
Bench - nightly toolchain (recent)	1m 25s
Lint - nightly toolchain (recent)	39s
Docs - nightly toolchain (recent)	18s
Embedded - nightly toolchain	3m 3s
	25m 21s

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