Allow configurable minimum fee-rate validation for TRUC txs

[landabaso]

• add an optional minimumFeeRate parameter to coinselect, addUntilReach, avoidChange, and maxFunds
• keep the default minimum at 0.1 sat/vB for backwards compatibility, while allowing zero or sub-0.1 fee rates for TRUC/package relay use cases
• add runtime tests for the default rejection path and the lowered-floor acceptance path@ and bump the package version to 2.0.1