Reduce memory used for balancer v2 liquidity

[MartinquaXD]

Description

The new driver is using a huge amount of memory. One low hanging fruit is to slightly redesign the internals of balancer v2 liquidity. Currently all those stable and weighted pools contain big pieces of data that don't change and are duplicated.
For other liquidity sources this was handled by having an Inner component that contains that data which is shared with Arcs across all liquidity components.

Changes

This PR applies that same pattern for balancer stable and weighted pools.

How to test

Just the compiler since it's only a minor refactor

[fleupold]

Love your branch names.

Do you have a slight indication/benchmark of how big this reduction is (e.g. on your local machine) that you could add to the PR description?

[MartinquaXD]

Went back over this optimization to supply a reasonable visualization of this improvement. For these graphs I applied the optimization on top of #2102 because it makes it easier to see its impact.

1. With optimizations of Reduce memory consumption of RecentBlockCache #2102

2. With this PR's optimization in addition we can see that the big but slim spikes are gone now. This is actually not the exact outcome I would have predicted but I take it. 😅