Break down contract fee (size) estimation with separation of responsibilities and update tests to match
For example, the code does:
- dummy oracle message
- dummy oracle sig
- dummy funding details
- builds a whole payout transaction with the dummy data
- measures the size of that tx
This is fine. But size estimation should probably be taking those parts or injecting the pieces to build it and just building the tx. Then the unit tests are basically:
- called buildtx with the available info
- return the size of that tx
The current test just says "631" which has no way to verify without spending a long time doing some custom setup. It might be fine as a trusted snapshot-type integration test.