Add Musig2 module #1578

Job	Run time
Test - 1.63.0 toolchain (minimal)	6m 9s
Format - nightly toolchain	14s
Docs - stable toolchain (recent)	22s
Test - 1.63.0 toolchain (recent)	6m 7s
Test 32-bit version	24s
Prepare	2s
Test - stable toolchain (minimal)	3m 38s
WASM - stable toolchain	1m 36s
Test - stable toolchain (recent)	3m 39s
Docs - nightly toolchain (recent)	27s
ASAN - nightly toolchain (recent)	1m 36s
Lint - nightly toolchain (recent)	30s
Bench - nightly toolchain (recent)	32s
Test - nightly toolchain (minimal)	2m 52s
no-std - nightly toolchain (recent)	47s
Test - nightly toolchain (recent)	2m 46s
	31m 41s

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