consider shipping the testnet3 cached RON in the repo

[dcdpr]

bitcoind_memo_testnet.ron is only 136KB.

If we attached this in the repo, then newbies could run the static integration tests without the networking hurdle, and see what this code delivers. (They would still immediately need to go back and fix the networking to take a next step with their personal data.)

Reducing this networking hurdle could really improve community engagement.

One thing we could do is compress all our existing RON files (eg. over in fixtures/wallets) and end up saving space while adding this testnet3 network data.

[parasyte]

This is really good for the offline story. We don't currently have (but easily can support) an offline bitcoin client that uses these RON files.

Some pointers for where to start:

• This is a client implementation that uses local files for resolving blockchain transactions (used in unit tests):

  taxcount/src/imports/wallet.rs

  Lines 796 to 818 in 8264524

  	impl MockClient {
  	pub(crate) fn new<P: AsRef<Path>>(file: P) -> Self {
  	let data = std::fs::read_to_string(file).expect("Could not open RON file");
  	ron::from_str(&data).expect("RON decoding error")
  	}
  	}
  	impl ClientApi for MockClient {
  	fn get_transactions(&self, txids: &[Txid]) -> HashMap<Txid, TxResult> {
  	txids
  	.iter()
  	.map(|txid| (*txid, Arc::new(Ok(self.tx[txid].clone()))))
  	.collect()
  	}
  	fn get_blocks(&self, block_hashes: &[BlockHash]) -> HashMap<BlockHash, BlockResult> {
  	block_hashes
  	.iter()
  	.map(|block_hash| (*block_hash, Arc::new(Ok(self.blocks[block_hash].clone()))))
  	.collect()
  	}
  	}

• This is the client enum with configurable implementations (currently only bitcoind and esplora APIs are supported):

  taxcount/src/client.rs

  Lines 17 to 24 in 8264524

  	/// Memoizing client that retrieves Bitcoin transactions and blocks.
  	///
  	/// All supported backends are guaranteed to memoize requests and provide per-resource concurrency,
  	/// limited by global threadpool configuration. See `cargo run -- --help`
  	pub enum Client {
  	Bitcoind(bitcoind::BitcoindClient),
  	Esplora(esplora::EsploraClient),
  	}

Adding a new local-file-based-resolver (similar to the one used in unit tests) to the enum is a good first step for making this happen.