[feature]: further test coverage for manual fee rates and fee rate estimation

[jharveyb]

Continuation of work from #595 , being implemented in #605 .

• change units for manual fees to sat/vB to better match LND etc.
• test negative cases for manual fees below the minimum fee, exceeding wallet funds
• negative cases for fee estimation exceeding wallet funds or excessively low estimate
• increase logging of fees used and TX weights
• investigate mis-adjustment of final absolute fees for anchor TXs for minting and transfers

[jharveyb]

Closed with #605.