Clean up budget cost types

[jayz22]

What

• Resolves Re-evaluate the necessity for all the contract cost types before testnet #981
• Also does follow up to Scale the linear cost model coefficient; improve model fitting #982, adding a ScaledU64 type and use it explicit for the linear cost parameter, which turned out to be a bigger-than-expected change that required changes to some existing types and interfaces in budget.
• Fixed a bug in cpu->fuel conversion and added a test.
• Did various budget metering related cleanups along the way.
• Recalibration. Here is the output

Why

[TODO: Why this change is being made. Include any context required to understand the why.]

Known limitations

[TODO or N/A]