Fix npm test runner on Windows

[cedar323]

Summary

• replace the POSIX-only npm test command with a small Node runner
• preserve the existing mocha options while allowing extra CLI arguments to pass through
• set NODE_ENV=test in a cross-platform way

Verification

• npm test -- test\errors\rpc-error_test.js --reporter spec passes on Windows
• git diff --check reports no patch whitespace errors; Git only warns that package.json/test/run-mocha.js will be normalized to CRLF locally

Note: npm run lint -- --quiet currently fails on pre-existing linebreak-style errors across the repository on Windows, unrelated to this change.

[MyTH-zyxeon]

Maintainer-facing review assist for the Bitgesell #39 bounty lane:

I checked current head 24f0ea2103500ff4dbfe42939cdfe7ae1724ce09. The diff is narrow: package.json switches the test script from the POSIX-only NODE_ENV=test mocha $npm_package_options_mocha form to node test/run-mocha.js, and the new runner sets NODE_ENV=test, invokes the local Mocha binary through node, preserves the existing Mocha options (--timeout 20000 --recursive --require should), and forwards extra CLI arguments.

Current visible state: PR is OPEN, MERGEABLE, mergeStateStatus=CLEAN, has no top-level comments or reviews, and no status checks are visible on the PR. It looks like a focused cross-platform test-runner fix rather than a runtime/client behavior change.

Pre-merge checks I would use:

1. Run the author's Windows command (npm test -- test\errors\rpc-error_test.js --reporter spec) plus the same targeted test on a POSIX shell to confirm argument forwarding stays equivalent.
2. Run npm test without extra args once, because the runner hardcodes the existing options.mocha value instead of reading npm_package_options_mocha dynamically.
3. Confirm npm run cover still works, since it shells through nyc ... npm test and will now call the node runner.

No claim/payment action from me here; this is just review-routing support so maintainers can evaluate #11 against the active Bitgesell PR bounty queue.