fix(rippled): switch to xrpllabsofficial image + isolate from mainnet UNL

[RomThpt]

Summary

Stacks on top of #10. Brings the canonical `rippled→rippled` sync sub-test to green and cleans up rippled's behaviour in a closed test network.

Why the previous rippled image was painful

`rippleci/rippled:develop` is a CI dev build that:

• loads `vl.ripple.com` / `vl.xrplf.org` (the mainnet validator UNL) by default → hundreds of `is_trusted: 0` validation messages from real mainnet validators flood our 2-node test consensus log
• carries the compiled-in PeerFinder bootcache so rippled aggressively tries real mainnet IPs (3.77.5.186, 35.158.172.184, …)
• a tx submitted with `tesSUCCESS` ended up stranded in open ledger because the local consensus circle was never able to close cleanly under that noise

Changes

1. Base image → `xrpllabsofficial/xrpld:latest` (3.1.2 stable). Debian based, runs as root, ships rippled release binaries. Smaller, faster to pull, predictable in a closed test net.
2. Empty `[validator_list_sites]` and `[validator_list_keys]` sections in `rippled.cfg` so rippled trusts only what's in `validators.txt` — i.e. the keys hive uploaded.
3. Retry `account_info` on the late joiner. rippled returns `noNetwork` while `server_state == connected` (validations seen but state not yet replayed). The previous code failed `account_info` immediately after `WaitForLedger` returned, racing rippled's catchup. Retry up to 120s; rxrpl answers on first call so the loop is a no-op for it.

Result on `--client rxrpl,rippled` (4 sub-tests)

Test	Before	After
`initial=rxrpl late=rxrpl`	✅	✅
`initial=rxrpl late=rippled`	❌	❌ (separate issue: rippled catch-up from rxrpl UNL)
`initial=rippled late=rxrpl`	✅	✅
`initial=rippled late=rippled`	❌	✅ — the canonical homogeneous case is now green, account state verified

3/4 sub-tests pass. The remaining failure is rippled-side catch-up from a non-rippled UNL — needs follow-up investigation, likely on the rippled side.

Test plan

• `go build ./simulators/sync/` clean
• `docker build clients/rippled/` builds successfully on arm64 (via Rosetta)
• `./bin/xrpl-hive --sim sync --client rxrpl` (single impl) still PASS
• `./bin/xrpl-hive --sim sync --client rxrpl,rippled` reports 4 sub-tests, 3 pass / 1 fail (the cross-impl rippled-catchup-from-rxrpl-UNL case)
• verified rippled log shows only `is_trusted: 1` validations from the 2 configured validators (no more mainnet noise)