feat: support bitcoin testnet4 network

[zoedberg]

Closes #497

This PR adds support for bitcoin testnet4. It uses the tip of Blockstream/electrs#144 as electrs commit in contrib/Dockerfile.base (available once the PR gets merged), let me know if that's ok or if you prefer to use the merge commit.

I haven't changed the files related to the public blockstream.info website since that feels like something you'll want to handle separately.

[philippem]

Please rebase and update with new-index tip after electrs commit from merge of Blockstream/electrs#144

[zoedberg]

Rebased on master (706488c) and changed electrs commit to the tip of new-index (fee74a0450bc28f50f89d8115c8434844088d469)

[zoedberg]

@philippem Rebased again on updated master (52de3cc)

[zoedberg]

Rebased again on updated master (746efd6)

[bitwalt]

ACK

[zoedberg]

@philippem Rebased again on updated master (4c2ebe1)

[zoedberg]

@philippem Rebased again on updated master (cf1595d). I would very appreciate if someone could merge this

[philippem]

[thanks for rebasing, just ran a test with docker as per instruction in readme (did docker build --no-cache) bitcoin complains on startup

4-Warning: /data/.bitcoin.conf:2 Section [testnet4] is not recognized.
4-
4-2025-10-27T15:01:48Z Ignoring unknown configuration value testnet4
4-2025-10-27T15:01:48Z Ignoring unknown configuration value testnet4.enforcenodebloom
4-2025-10-27T15:01:48Z Bitcoin Core version v27.2.0 (release build)
4-2025-10-27T15:01:48Z Warning: /data/.bitcoin.conf:2 Section [testnet4] is not recognized.
4-

bitcoin version in dockerfile is 27.2 but testnet4 support was added in testnet4. can you test with a newer version of bitcoin core? (28.2)

[zoedberg]

@philippem Nice catch, thank you. PR updated, it now includes the bump of bitcoind from version 27.2 to 28.2

Commands to rebuild:

docker build --no-cache -t esplora-base:latest -f contrib/Dockerfile.base .
docker tag esplora-base:latest blockstream/esplora-base:latest # caution, this will shadow the official image from docker hub
docker build --no-cache -t esplora -f contrib/Dockerfile .

[philippem]

running full regression (with bitcoin core update).