Add flask-hmr: Flask CLI alternative with Hot Module Reloading

[Copilot]

This PR implements flask-hmr, a Flask CLI alternative that provides Hot Module Reloading capabilities similar to uvicorn-hmr but specifically designed for WSGI applications.

What's New

🚀 flask-hmr Package

A new CLI tool that replaces the standard flask run command with HMR capabilities:

# Instead of: flask run --reload
flask-hmr app:app

# With custom options
flask-hmr --host 0.0.0.0 --port 8080 --clear app:app

Key Features

• Hot Module Reloading: Only reloads changed modules and their dependents, not the entire application
• Flask-Native: Uses Werkzeug development server (Flask's default)
• uvicorn-hmr Compatible: Same CLI interface and behavior patterns
• Efficient Development: Avoids slow application restarts during development

CLI Options

The tool supports all major options from uvicorn-hmr adapted for Flask:

• --host / --port: Server binding configuration
• --reload-include / --reload-exclude: File watching control
• --clear: Clear terminal before restarting server
• --env-file: Environment file loading
• --log-level: Logging configuration

Example Usage

Consider a Flask app with a slow-loading ML model:

# app.py
from flask import Flask
import heavy_ml_model  # Takes 5 seconds to load

app = Flask(__name__)

@app.route("/")
def hello():
    return "Hello World!"

Before (with flask run --reload): Every code change triggers a full restart, waiting 5 seconds each time.

After (with flask-hmr): Route changes reload instantly without reinitializing the ML model.

Integration

• Updated Flask example to demonstrate flask-hmr usage
• Added to workspace configuration for proper dependency management
• Comprehensive documentation with usage examples
• Full test coverage including HMR functionality, error handling, and edge cases

Implementation Details

The implementation follows the same patterns as uvicorn-hmr:

• Uses typer for CLI interface
• Integrates with reactivity.hmr.core for hot reloading
• Extends SyncReloader for file watching
• Provides proper error handling and recovery

This completes the Flask integration requested in the issue, providing a production-ready alternative to Flask's built-in development server with advanced HMR capabilities.

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[hyperlint-ai-deprecated]

PR Change Summary

Implemented a Flask CLI alternative with Hot Module Reloading (HMR) capabilities, similar to uvicorn-hmr, enhancing the development experience for WSGI applications.

• Created the flask-hmr package to provide a CLI tool for Flask applications with HMR features.
• Integrated Werkzeug development server for improved compatibility with Flask.
• Added support for key CLI parameters including host, port, and reload options.
• Updated documentation to reflect new CLI usage and options.

Modified Files

• examples/flask/README.md

Added Files

• packages/flask-hmr/README.md

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