v1: Flet CLI: Add flet serve command to run HTTP server with WASM support

[FeodorFitsner]

usage: flet serve [-h] [-v] [--port PORT]
                  [--web-root WEB_ROOT]

Serve static files from a directory with optional WASM
headers.

options:
  -h, --help           show this help message and exit
  -v, --verbose        -v for detailed output and -vv for more
                       detailed
  --port PORT          Port to serve on (default: 8000)
  --web-root WEB_ROOT  Directory to serve (default:
                       ./build/web)

Summary by Sourcery

Add a "serve" command to the Flet CLI for hosting static files over HTTP with WebAssembly-friendly headers and configurable port and web root options.

New Features:

• Add "flet serve" command to serve static files with COOP, COEP, and CORS headers
• Allow users to specify server port and web root directory
• Handle directory validation, keyboard interrupts, and OS errors with user-friendly messages

[sourcery-ai]

We've reviewed this pull request using the Sourcery rules engine

[ndonkoHenri]

LGTM