[Refactor] Simplify parseEnvNumber helper in environment module

[gonzaloriestra]

WHY are these changes introduced?

Fixes #0000

In packages/cli-kit/src/public/node/environment.ts, parseEnvNumber called Number(value) twice whenever a valid numeric string was provided and used the legacy global isNaN() function instead of standard Number.isNaN().

WHAT is this pull request doing?

Refactors parseEnvNumber in environment.ts to:

• Early return undefined for empty/falsy inputs
• Compute Number(value) once
• Use standard Number.isNaN to check for invalid numbers

How to manually test your changes?

CI

Post-release steps

Checklist

• I've considered possible cross-platform impacts (Mac, Linux, Windows)
• I've considered possible documentation changes
• I've considered analytics changes to measure impact
• The change is user-facing — I've identified the correct bump type (patch for bug fixes · minor for new features · major for breaking changes) and added a changeset with pnpm changeset add

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PR created automatically by Jules for task 12271033484687374892 started by @gonzaloriestra

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