Promote prefer-promise-reject-errors to error and fix violations

[joehan]

Description

This PR resolves all remaining violations of the ESLint prefer-promise-reject-errors rule and promotes the rule from "warn" to "error" in .eslintrc.js.

Changes Made

• src/emulator/commandUtils.ts: Pass getError(e) in processKillSignal, and use FirebaseError when child process errors or exits with a signal in runScript.
• src/emulator/dataconnectEmulator.ts: Reject with a descriptive FirebaseError when failing to connect to the SQL Connect emulator.
• src/emulator/eventarcEmulator.ts: Reject with a FirebaseError when functions emulator is missing in triggerEventFunction.
• src/profileReport.ts: Reject readline error with the original Error or wrapped FirebaseError.
• src/emulator/workQueue.spec.ts: Reject with new Error("job failed") in test.
• src/throttler/throttler.spec.ts: Reject with new Error("retry") in retry test.
• src/utils.spec.ts: Add explicit eslint-disable-next-line prefer-promise-reject-errors annotations where tests intentionally test rejection handling with non-Error values ("bar", "fail fast").
• .eslintrc.js: Promote prefer-promise-reject-errors from "warn" to "error".

Verification

• npm run build passed completely (build:mcp-apps, tsc, copyfiles).
• npx mocha passed across all modified/affected spec files (commandUtils.spec.ts, workQueue.spec.ts, profileReport.spec.ts, throttler.spec.ts, utils.spec.ts).
• ESLint passed on all modified files with 0 errors and 0 warnings.
• Prettier check passed on all modified files.

Related Bug: b/565074829

[gemini-code-assist]

Code Review

This pull request configures the ESLint rule prefer-promise-reject-errors to trigger an error instead of a warning, and updates various emulator and utility files to reject promises with proper Error or FirebaseError instances. Feedback on the changes suggests avoiding the as any type assertion in src/profileReport.ts by wrapping non-Error values in a new Error object, and utilizing the existing getError utility in src/emulator/commandUtils.ts to simplify error handling.

[joehan]

Just remove this entirely and fall back to the default value

[joehan]

Removed prefer-promise-reject-errors completely from .eslintrc.js to fall back to the preset default ("error") in commit 696801bbc. Verified with npm run test:compile, npx mocha, and full-repo npm run lint:quiet.