fuzz: add chanmon holder signer fuzz ops #23489

Job	Run time
benchmark	17m 41s
linting	2m 37s
tor-connect	7m 12s
check_docs	7m 28s
fuzz	1h 27m 56s
check_release	3m 9s
rustfmt	15s
fuzz_sanity	9m 31s
ext-test	6m 44s
build-cfg-flags / build (self-hosted, 1.75.0)	12m 50s
build-features / build (self-hosted, 1.75.0)	34m 10s
build-bindings / build (self-hosted, 1.75.0)	18m 1s
build-nostd / build (self-hosted, 1.75.0)	13m 53s
build-workspace / build (self-hosted, 1.75.0)	12m 10s
build-sync / build (self-hosted, 1.75.0)	21m 6s
coverage	0s
notify-failure	0s
	4h 14m 43s

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