Add Musig2 module #1542

Job	Run time
Test - stable toolchain (minimal)	3m 58s
Test - 1.63.0 toolchain (minimal)	5m 22s
Test - stable toolchain (recent)	3m 51s
Test - 1.63.0 toolchain (recent)	5m 24s
Test 32-bit version	25s
Docs - stable toolchain (recent)	18s
Format - nightly toolchain	11s
Prepare	5s
WASM - stable toolchain	1m 53s
Lint - nightly toolchain (recent)	26s
Test - nightly toolchain (minimal)	2m 50s
Test - nightly toolchain (recent)	2m 43s
Bench - nightly toolchain (recent)	23s
ASAN - nightly toolchain (recent)	1m 22s
Docs - nightly toolchain (recent)	17s
no-std - nightly toolchain (recent)	56s
	30m 24s

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