feat: implement bitcoin-regtest-up runtime installer

[ulissesferreira]

Summary

This PR is the second of two PRs splitting #8827, stacked on top of:

• feat: scaffold @metamask/bitcoin-regtest-up package #9211 — scaffold: feat: scaffold @metamask/bitcoin-regtest-up package

It contains only the real implementation of the Bitcoin Core regtest runtime installer, with no unrelated monorepo changes.

What's included (delta vs scaffold PR)

• src/install.ts — core Bitcoin Core download, SHA-256 checksum verification, extraction, and install logic (pinned to Bitcoin Core 30.2)
• src/bin/bitcoin-regtest-up.ts — CLI entry point (registered as bin in package.json)
• src/index.ts — updated exports
• src/install.test.ts — Jest tests for the installer (11 tests covering download, verify, cache reuse, alternate binary layouts, cache clean)
• src/index.test.ts — removed (replaced by install tests)
• package.json — adds bin field + version bump to 0.1.0
• CHANGELOG.md — changelog entry for the initial implementation
• README.md — full usage documentation
• jest.config.js — updated for the new test structure (relaxed coverage thresholds, CLI entry excluded)
• yarn.lock — updated for any new deps

What's NOT included

No knip.config.ts changes, no CODEOWNERS/teams.json churn (those are in the scaffold PR), no unrelated monorepo changes.

Replaces

Together with #9211, this replaces #8827 with two clean, reviewable PRs based on current origin/main.

Verification

yarn workspace @metamask/bitcoin-regtest-up run build
yarn workspace @metamask/bitcoin-regtest-up run test
yarn eslint packages/bitcoin-regtest-up
yarn constraints
yarn workspace @metamask/bitcoin-regtest-up run changelog:validate
yarn dedupe --check

All passed ✓

---

Note

Low Risk
New dev/CI tooling package with checksum-verified downloads and no changes to production wallet or auth paths; main risk is incorrect binary wiring or cache behavior in local/CI environments.

Overview
Replaces the scaffold placeholder with a runtime-only Bitcoin Core installer for E2E/dev: consumers run bitcoin-regtest-up install (or default) to download a pinned 30.2 archive per platform, verify SHA-256, extract into .metamask/cache (or ~/.cache/metamask when Yarn enableGlobalCache is true in parsed .yarnrc.yml), and write node_modules/.bin/bitcoind and bitcoin-cli Node wrappers that forward args and propagate non-zero exits/signals.

The bitcoin-regtest-up CLI also supports cache clean (namespace-only), --help, and flags for cache/bin dirs, platform override, and URL/checksum overrides. package.json keys bitcoinRegtestUp / variants merge partial bitcoinCore overrides with defaults; missing package.json is tolerated for flag-only flows.

install.ts handles alternate archive layouts (bitcoind, bitcoin-node, bitcoin + node subcommand), cache reuse with runnable-binary checks, stale symlink replacement, and injectable download/extract for tests. Docs, changelog, yaml dependency, relaxed Jest coverage (CLI entry ignored), and broad install.test.ts coverage accompany the bin registration.

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There are 2 total unresolved issues (including 1 from previous review).

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