Add Musig2 module #1536

Job	Run time
Test 32-bit version	29s
Docs - stable toolchain (recent)	14s
Format - nightly toolchain	14s
Test - 1.63.0 toolchain (minimal)	5m 28s
Prepare	5s
Test - stable toolchain (minimal)	3m 53s
Test - 1.63.0 toolchain (recent)	5m 21s
Test - stable toolchain (recent)	4m 38s
WASM - stable toolchain	2m 14s
Test - nightly toolchain (minimal)	2m 46s
Bench - nightly toolchain (recent)	20s
Test - nightly toolchain (recent)	2m 47s
ASAN - nightly toolchain (recent)	1m 26s
Docs - nightly toolchain (recent)	16s
Lint - nightly toolchain (recent)	23s
no-std - nightly toolchain (recent)	41s
	31m 15s

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