Pre-calculate heap element scores (retaining RouteGraphNode size)

[rust-lightning] / pending_changelog / route-blinding-intro-node.txt

## Backwards Compat

* Forwarding a blinded HTLC and subsequently downgrading to an LDK version prior to 0.0.119 may
        result in a forwarding failure or an HTLC being failed backwards with an unblinded error.