Pull latest cost models from fetcher

[jinglescode]

Describe the feature you'd like

As hardfork cost model changes seems to become more common, and as each network can have different cost models. Its time to pull cost models when building transactions.

Is your feature request related to a problem? Please describe.

Whenever cost model changes, need to update cost model manually will result in down time.

Describe the solution you'd like

With fetcher provided, fetch cost model for the network it is using. If setNetwork is provided, then we can differentiate between preview and preprod if they have different cost models.

Additional context

No response

Would you be willing to implement it?

• Yes, I will implement it.

[twwu123]

Most likely the behaviour I'm aiming for is to pull cost models from fetcher if fetcher instance is provided. ONLY IF fetcher instance is not provided, I will use default values for the network.