refactor: move `SignSignature` helpers to test utils #231

Job	Run time
ASan + LSan + UBSan + integer, no depends, USDT	1h 4m 50s
macOS 13 native, x86_64, no depends, sqlite only, gui	52m 32s
Win64 native, VS 2022	2h 27m 35s
test each commit	0s
	4h 24m 57s

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