feat: Add new parallel_chat() feature

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Pull Request Overview

This PR adds new parallel chat functionality to enable concurrent processing of multiple prompts. The implementation provides three main functions: parallel_chat() for returning full Chat objects, parallel_chat_text() for text-only responses, and parallel_chat_structured() for extracting structured data using Pydantic models.

• Implements rate limiting and concurrency controls for API requests
• Adds comprehensive test coverage for basic chat, tool usage, and structured data scenarios
• Integrates the new functionality into the main package exports

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
chatlas/_parallel.py	Core implementation of parallel chat functions with rate limiting and progress tracking
chatlas/_chat.py	Added kwargs parameter support to structured data extraction methods
chatlas/__init__.py	Exported new parallel chat functions in package API
tests/test_parallel_chat.py	Comprehensive test suite covering all parallel chat functionality
CHANGELOG.md	Documentation of new feature addition

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