test(regnet): isolate tests and refresh mainnet seeds

[pig-g]

Summary

• add explicit --config-custom, --regnet-dir, --wallet-file, --bind, and ownership-token node startup options
• run pytest against a loopback-only regnet with temporary databases, application logs, subprocess output, and wallet keys
• replace the fixed startup sleep with a bounded real RPC readiness probe tied to the spawned node by a unique token
• guarantee spawn-failure, startup-failure, terminate/kill, environment restoration, and temporary-file cleanup
• make regtest_generate(N) retry until exactly N blocks are created or fail
• remove the broken bismuthcore test dependency while preserving transaction signature verification
• add a pinned Python 3.11 dependency graph, a guarded one-command clean runner, and immutable-action GitHub Actions coverage
• replace stale mainnet seeds with nine public nodes verified through two consecutive read-only RPC rounds
• list the maintained Terranbase Bismuth explorer

Mainnet metadata refresh

• queried candidate nodes with BismuthClient getversion and statusjson; no mutable RPC was used
• retained exactly nine IPv4 global-unicast nodes on port 5658 that responded in both rounds
• observed all nine synchronized at block 4,914,895 with allowed mainnet0021, mainnet0022, or mainnet0023 protocol versions
• made peers.txt and suggested_peers.txt the same curated fallback set so stale candidates are not reintroduced
• added https://bismuth1.terranbase.xyz, verified over HTTPS with recent blocks matching the live-node sequence
• added offline regressions for exact seed count, JSON parity, port, IPv4 global-unicast scope, and explorer documentation

Safety boundaries

• defaults regnet to 127.0.0.1 and explicitly binds the test node there
• loads tests/config_custom.txt explicitly (regnet=True, no mainnet peer path)
• rejects a missing explicit custom config or a regnet datadir paired with mainnet settings
• redirects ledger, index, peers, wallet, application log, and subprocess output into a pytest temporary directory
• fails immediately if port 3030 already has a listener; readiness additionally requires the spawned node's random RPC token
• cleans process, environment variable, database, peer, wallet, and log state after the suite
• keeps the legacy node.py regnet2 positional form parse-compatible
• refuses to clear a symlinked or non-virtualenv .venv

Verification

• ./scripts/test_regnet.sh — 60 passed in a newly recreated Python 3.11 venv
• original suite only — 26 passed
• regnet runtime and metadata regressions — 34 passed
• test_api_getaddresssince — passed in three independent regnet sessions
• repository node.log SHA-256 unchanged across fixture execution
• malicious .venv symlink guard — passed; target marker preserved
• post-suite 127.0.0.1:3030 — closed (connect_ex=111)
• python3 -m compileall — passed
• shellcheck scripts/test_regnet.sh — passed
• git diff --check — passed
• added-line security scan — no secrets, shell injection, eval/exec, pickle, or SQL formatting findings
• post-fix independent review — passed=true, security concerns 0, logic errors 0, suggestions 0

Closes pig-g#1

[hclivess]

Can you cross open PR on https://github.com/hclivess/Bismuth ? Most of these may not be relevant anymore