Implement bridge_cost for CachingOptimizer

[blegat]

Abstract description

Consider layers: LazyBridgeOptimizer(Dualization(LazyBridgeOptimizer)) (with possible caching layers in between).
If you have a set S that does not implement dual_set but that has bridges, then a constraint F-in-S with this set are not supported by the dualization layer so it will be bridged by the outer layer. Now, all the other constraints that ##are supported by dualization will just go through the dualization layer will bridging cost of 0, even though they may be bridged by the inner bridges. Because of this, the bridge choice for F-in-S will be completely blind and might be sub-optimal.

Concrete example

The whole idea detailed in jump-dev/SumOfSquares.jl#205 explains that we have a KernelBridge and an ImageBridge and the right one will be picked thanks to the bridge cost

Written by Claude, I haven't checked yet