feat: add JEST_MAX_WORKERS environment variable support

[vitorveiga]

Summary

• Adds support for setting maxWorkers via the JEST_MAX_WORKERS environment variable
• Provides a convenient way to control worker count in CI environments without modifying configuration files or CLI arguments
• Supports both numeric values (e.g., "4") and percentage-based values (e.g., "50%")

Changes

• packages/jest-config/src/getMaxWorkers.ts: Added check for process.env.JEST_MAX_WORKERS in the resolution priority chain
• packages/jest-config/src/__tests__/getMaxWorkers.test.ts: Added 5 new unit tests covering the environment variable functionality, priority order, and percentage support
• docs/Configuration.md: Updated the maxWorkers documentation section to explain the priority order and usage of JEST_MAX_WORKERS

Priority Order

The maxWorkers option is now resolved in the following order:

1. argv.maxWorkers (CLI argument)
2. defaultOptions.maxWorkers (configuration file)
3. process.env.JEST_MAX_WORKERS (environment variable) ⬅️ new
4. CPU-based defaults

Test Plan

• Built the project with yarn build:js
• Linted modified files (no errors)
• All 12 unit tests in getMaxWorkers.test.ts pass, including 5 new tests for the environment variable
• Verified environment variable supports numeric and percentage values
• Verified priority order is respected

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• ✅ login: vitorveiga / name: vitorveiga (66d1082, a565c1a)

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commit: 66d1082