Add a protocol-aware note fee policy

`BasicConstantFeePolicy` should remain simple and charge a fixed fee per note script. Instead of adding asset-based pricing to it, introduce a separate policy that estimates the protocol cost of a note.

The policy should:

- store `lookup_key |-> worst_case_cycles` in its fee schedule;
- account for note properties such as the number of assets and storage requirements;
- apply the reference block’s fee parameters to estimate the protocol fee; and
- scale the result by a configured constant.

This replaces the asset-count extension proposed in #3393. The experimental implementation in #3429 can be closed.