Refactor the default feeRate of rgbpp-sdk/btc

[Flouse]

Tune the default fee_rate of a btc transaction to the fastestFee of curl -sSL "https://mempool.space/api/v1/fees/recommended".

Related Code

https://github.com/ckb-cell/rgbpp-sdk/blob/44b8eda57b5a51a0a7b9a0ebd181b19d5e8db2c6/packages/btc/src/query/source.ts#L153-L161

https://github.com/ckb-cell/rgbpp-sdk/blob/44b8eda57b5a51a0a7b9a0ebd181b19d5e8db2c6/examples/rgbpp/local/transfer-btc.ts#L34-L35

[ShookLyngs]

Two questions:

1. Do you wish all APIs to use the fastestFee?
2. Do you prefer an option (e.g. feeType, recommendedFeeType) to adjust the fee rate?

[Flouse]

• Do you wish all APIs to use the fastestFee?

1. Yes, use mempool.space API's fastestFee by default if the param feeRate is not specified.

• Do you prefer an option (e.g. feeType, recommendedFeeType) to adjust the fee rate?

2. LGTM. Do you mean supports feeRate: number | recommendedFeeType | undefined?

[ShookLyngs]

2. LGTM. Do you mean supports feeType: number | recommendedFeeType?

I was thinking maybe we can add a prop in the APIs (feeType or recommendedFeeType):

sendBtc({
  ...
  feeRate: 1, // optional, default to undefined
  feeType: 'halfHourFee', // optional, if "feeRate == undefined", use FeesRecommended[feeRate] as the fee rate
});