Add Musig2 module #1517

Job	Run time
Test 32-bit version	59s
Docs - stable toolchain (recent)	11s
Test - 1.63.0 toolchain (minimal)	6m 9s
Format - nightly toolchain	15s
Test - 1.63.0 toolchain (recent)	6m 8s
Prepare	4s
Test - stable toolchain (minimal)	4m 0s
WASM - stable toolchain	1m 56s
Test - stable toolchain (recent)	3m 51s
Docs - nightly toolchain (recent)	19s
Test - nightly toolchain (minimal)	2m 51s
Lint - nightly toolchain (recent)	23s
Test - nightly toolchain (recent)	2m 46s
ASAN - nightly toolchain (recent)	1m 30s
Bench - nightly toolchain (recent)	20s
no-std - nightly toolchain (recent)	43s
	32m 25s

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