feat(rgbpp-sdk/btc): add mempool.space api to provide default fee rate

[ShookLyngs]

Changes

• Add DataSource.getRecommendedFeeRates and DataSource.getAverageFeeRate APIs
• When the feeRate prop in TxBuilder is undefined, get a fee rate from DataSource.getAverageFeeRate

Details

The getRecommendedFeeRates API returns a FeesRecommended object, which offers several levels of fee rates for users to choose from. The overall ranking on satoshi costing from high to low, or confirm time spent from fastest to slowest, is as follows:

fastestFee > halfHourFee > economyFee > hourFee > minimumFee > minimumFee

On the other hand, the getAverageFeeRate API returns the halfHourFee. This means that if the user leaves the feeRate empty while initializing a TxBuilder, it uses the halfHourFee as the default fee rate.

Types

getRecommendedFeeRates and getAverageFeeRate:

interface DataSource {
  // ... other apis
  getRecommendedFeeRates(): Promise<FeesRecommended>;
  getAverageFeeRate(): Promise<number>;
}

FeesRecommended:

interface FeesRecommended {
  fastestFee: number;
  halfHourFee: number;
  hourFee: number;
  minimumFee: number;
}