Add Musig2 module #1539

Job	Run time
Test - 1.63.0 toolchain (minimal)	1m 55s
Docs - stable toolchain (recent)	14s
Test - 1.63.0 toolchain (recent)	1m 45s
Test 32-bit version	25s
Format - nightly toolchain	12s
Prepare	4s
Test - stable toolchain (minimal)	39s
WASM - stable toolchain	2m 1s
Test - stable toolchain (recent)	46s
Docs - nightly toolchain (recent)	29s
Lint - nightly toolchain (recent)	23s
Bench - nightly toolchain (recent)	19s
Test - nightly toolchain (minimal)	51s
Test - nightly toolchain (recent)	1m 2s
ASAN - nightly toolchain (recent)	1m 24s
no-std - nightly toolchain (recent)	39s
	13m 8s

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