Add Musig2 module #1519

Job	Run time
Prepare	3s
Test 32-bit version	38s
Docs - stable toolchain (recent)	16s
Format - nightly toolchain	13s
Test - 1.63.0 toolchain (minimal)	6m 5s
Test - stable toolchain (minimal)	3m 58s
Test - 1.63.0 toolchain (recent)	6m 14s
Test - stable toolchain (recent)	3m 58s
WASM - stable toolchain	2m 9s
Lint - nightly toolchain (recent)	24s
ASAN - nightly toolchain (recent)	1m 32s
Bench - nightly toolchain (recent)	31s
Docs - nightly toolchain (recent)	21s
Test - nightly toolchain (minimal)	2m 49s
Test - nightly toolchain (recent)	2m 52s
no-std - nightly toolchain (recent)	42s
	32m 45s

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