fix(task-refactor): add explicit on/off methods to ITask interface

[akulakum]

COMPLETES #https://jira-eng-sjc12.cisco.com/jira/browse/CAI-7779

This pull request addresses

1. Missing on()/off() type declarations on ITask interface

As part of the task-refactor, the SDK's ITask interface extends Node's EventEmitter for on()/off() methods, but consumers like CC Widgets whose tsconfig.json restricts type resolution to "types": ["jest"] cannot resolve @types/node — resulting in TS2339: Property 'on'/'off' does not exist on type 'ITask' errors on every task.on() / task.off() call.

2. Named exports unreachable from the SDK's main entry point

The SDK's package.json maps "main" and "exports" to dist/webex.js, which only exported the Webex class as default. All named exports (TASK_EVENTS, getDefaultUIControls, AGENT_EVENTS, ContactCenter, etc.) were properly defined in dist/index.js but unreachable at runtime for consumers using import { TASK_EVENTS } from '@webex/contact-center'.

TypeScript compilation passed because types resolved from dist/types/index.d.ts, masking the fact that the runtime values were undefined. This caused the CC Widgets' addEventListeners() to crash silently on agent:dnRegistered, meaning no task event listeners (task:incoming, agent:stateChange, etc.) were ever registered — breaking incoming task rendering, modal popups, and RONA state updates.

by making the following changes

Fix 1: Self-contained ITask event methods

• Added explicit on() and off() method declarations directly on the ITask interface, making it self-contained so consumers no longer depend on @types/node to resolve EventEmitter methods
• Used (...args: any[]) => void for the listener parameter to match Node's EventEmitter signature and avoid type narrowing issues with existing consumer callbacks

Fix 2: Re-export named exports from webex.js

• Added export * from './index' in src/webex.js so that all named exports from index.ts (enums, functions, classes, and constants) are forwarded through the main entry point (dist/webex.js)
• This ensures import { TASK_EVENTS, getDefaultUIControls, AGENT_EVENTS } from '@webex/contact-center' resolves correctly at runtime, not just at compile time

Change Type

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update
• Tooling change
• Internal code refactor

The following scenarios were tested

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[Kesari3008]

Why do we need this change ? If this was a problem then how did we have widgets working till now ?