Add EMAIL parameter type for email validation

[sushilk123]

Add EMAIL parameter type for email validation

This PR adds a new EmailParamType to Click for validating email addresses in command-line applications.

Features

• ✅ Email validation using a simple but effective regex pattern
• ✅ Clear error messages for invalid email addresses
• ✅ Consistent API following existing parameter type patterns
• ✅ Comprehensive tests covering valid/invalid cases and edge cases
• ✅ Example usage demonstrating the EMAIL type
• ✅ Proper documentation with version info

Usage

python
import click

@click.command()
@click.option('--email', type=click.EMAIL)
def send_message(email):
click.echo(f"Sending to: {email}")

Validation Examples

• ✅ user@example.com
• ✅ test.email+tag@domain.co.uk
• ❌ invalid-email → "is not a valid email address"
• ❌ user@ → "is not a valid email address"

Implementation Details

• Follows the same patterns as existing types like UUID
• Uses a simple but effective regex: ^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$
• Includes proper error handling, whitespace trimming, and type conversion
• Comprehensive test suite with 6 test functions covering all scenarios

Files Changed

• src/click/types.py - Added EmailParamType class and EMAIL constant
• src/click/__init__.py - Exported EMAIL for public API
• tests/test_types.py - Added comprehensive test suite
• examples/email_example.py - Added usage example

This addresses the common need for email validation in CLI applications while maintaining Click's design principles.

[ThiefMaster]

I don't think this is useful in click. If someone needs this, they can implement this in their application and use a proper email validator. I'm quite certain that the current regex excludes valid emails, e.g. anything containing iternational domain names.

[ThiefMaster]

(I also have the feeling this PR is AI-generated. Don't do that.)