Introduce Dummy Hop support for Blinded Payment Path #21171

Job	Run time
benchmark	16m 38s
build (self-hosted, stable)	1h 39m 30s
build (self-hosted, 1.75.0)	1h 19m 17s
build (windows-latest, stable)	2h 26m 5s
ext-test	7m 53s
build (self-hosted, beta)	1h 17m 13s
build-tx-sync (ubuntu-latest, beta)	4m 40s
build-tx-sync (ubuntu-latest, stable)	4m 25s
build (macos-latest, 1.75.0)	2h 0m 58s
check_docs	3m 45s
build (macos-latest, stable)	2h 16m 46s
check_release	2m 49s
build-tx-sync (macos-latest, stable)	7m 18s
build-tx-sync (macos-latest, 1.75.0)	5m 12s
build-tx-sync (macos-latest, beta)	7m 10s
linting	2m 14s
rustfmt	17s
fuzz	1h 16m 47s
build-tx-sync (ubuntu-latest, 1.75.0)	5m 31s
coverage	39m 19s
	14h 3m 47s

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