Add support for musig() key expressions #1124

Job	Run time
Compilation for NanoS, X, S+, and Stax (nanos, $NANOS_SDK)	1m 43s
Compilation for NanoS, X, S+, and Stax (nanox, $NANOX_SDK)	1m 54s
Compilation for NanoS, X, S+, and Stax (nanosp, $NANOSP_SDK)	1m 47s
Compilation for NanoS, X, S+, and Stax (stax, $STAX_SDK)	1m 53s
Tests (nanos)	8m 19s
Unit test	1m 57s
Tests (nanox)	8m 22s
Tests with the JS library	1m 27s
Tests (nanosp)	8m 22s
Tests (stax)	8m 23s
Tests on mainnet (nanos)	33s
Tests with the Python library and legacy Bitcoin app	47s
Tests on mainnet (nanox)	36s
Tests on mainnet (nanosp)	37s
Tests on mainnet (stax)	31s
Tests for rust client library	1m 38s
	48m 49s

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