feat: implement getRgbppSpvProof for OfflineBtcAssetsDataSource

[fghdotio]

This feature allows users to provide SPV proofs when initializing the OfflineBtcAssetsDataSource, serving as a backup method for the BtcAssetsApi's cron job to unlock BTC time locked cells. This basically completes the core functionality of the OfflineBtcAssetsDataSource.

[duanyytop]

Please provide the CKB transaction hash to unlock the example's BTC time cell and run npx changeset to provide changeset like: https://github.com/utxostack/rgbpp-sdk/pull/297/files#diff-28110420e90e7b83c6a0b8b5112495f36a42bb30354d2f9d83b3578394aeb6e8R1

[fghdotio]

In this CKB transaction (link), an sUDT token, which was locked by a BTC time lock and could not be unlocked by the btc-assets-api's cron job, was unlocked using the provided example code.

[duanyytop]

In this CKB transaction (link), an sUDT token, which was locked by a BTC time lock and could not be unlocked by the btc-assets-api's cron job, was unlocked using the provided example code.

got it. The rgbpp-sdk and btc-assets-api only support xUDT and xUDT-compatible assets, so the sUDT assets will not be unlocked by btc-assets-api.

[fghdotio]

Fixed offline examples in this commit c4bd798.