refactor: remove utils.allSettled polyfill in favor of native Promise.allSettled

[kyungseopk1m]

Description

Removes the custom allSettled polyfill from src/utils.ts and replaces all call sites with the native Promise.allSettled.

Motivation

The polyfill was introduced to support Node.js versions below 12.9.0, where Promise.allSettled was not yet available. The source comment made this intent explicit:

// TODO: delete once min Node version is 12.9.0 or greater

The minimum Node.js version requirement is now >=20.0.0, as declared in package.json (engines field) and enforced at runtime in src/bin/firebase.ts. This far exceeds the 12.9.0 threshold, making the polyfill dead code.

This is the same pattern as several recent cleanups in the repo (e.g. cloneDeep TODO comments also targeting a minimum-version gate).

Changes

• Removed PromiseFulfilledResult, PromiseRejectedResult, PromiseResult type exports and allSettled function from src/utils.ts
• Removed corresponding unit tests for the polyfill from src/utils.spec.ts
• Updated all 8 call sites across the codebase to use Promise.allSettled directly:
  • src/emulator/functionsEmulator.ts
  • src/functions/secrets.ts
  • src/commands/ext-dev-deprecate.ts
  • src/commands/ext-dev-undeprecate.ts
  • src/deploy/functions/validate.ts
  • src/deploy/functions/release/fabricator.ts (×3 call sites)
  • src/deploy/functions/release/reporter.ts
• The PromiseRejectedResult cast in fabricator.ts now resolves against the TypeScript standard lib type rather than the removed local definition — no behavior change

Testing

• npx tsc --noEmit passes with no errors
• Existing tests unaffected; the removed test block covered only the polyfill's own implementation, not any business logic

[gemini-code-assist]

Code Review

This pull request replaces the custom utils.allSettled polyfill with the native Promise.allSettled implementation across several files, including the fabricator, reporter, and emulator components, and removes the now-obsolete tests and utility definitions. A review comment identifies that the removal in src/utils.ts left behind dangling comments and ESLint directives, and suggests refactoring or unifying another similar implementation (promiseAllSettled) still present in the file to avoid duplication.

[kyungseopk1m]

removed CHANGELOG entry and resolved conflicts with main.