Pass `EffectiveCapacity` through to scorer instead of a `u64`

Pass `EffectiveCapacity` through to scorer instead of a `u64`

There is little reason to take the `EffectiveCapacity`, which has
a bunch of information about the type of channel, and distill it
down to a `u64` when scoring channels.

Instead, we here pass the full information we know, in the form of
the original `EffectiveCapacity`. This does create more branching
in the main router loop, which appears to have a very slight (1-2%)
performance loss, but that may well be within noise.

Much more importantly, this resolves a panic in our log
approximation where we can accidentally call `log(0)` when the
channel's effective capacity is `u64::max_value()`.