Reject malformed integer environment variables

[mukeshr06]

WIREIT_PARALLEL and WIREIT_CACHE_MAX_ENTRIES use parseInt, so malformed values such as 2abc are silently accepted as 2. This can hide a configuration error instead of reporting the documented positive-integer requirement.

Parse the complete decimal value for both options and reject nonpositive or unsafe integers. Preserve surrounding whitespace, an optional leading +, leading zeroes, and the existing case-insensitive infinity handling.

The new user-facing regressions fail on the previous implementation and pass with this change. Compatibility cases run through npm, node --run, Yarn Classic, and pnpm; the original cache-limit case remains covered.

Validation on Node.js 24.19.0 (with node_modules/.bin on PATH):

• Build, ESLint, Prettier, and git diff --check: passed.
• Full CLI options suite: 92 passed, 4 intentional skips.
• New invalid-usage regressions: 2 passed.
• The full errors-usage suite has 7 existing IPC cleanup failures on this Node version. A baseline comparison reproduces the same 7 failures; only the two new malformed-value failures are fixed here.

[google-cla]

Thanks for your pull request! It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

View this failed invocation of the CLA check for more information.

For the most up to date status, view the checks section at the bottom of the pull request.