Summary

This PR moves all Netty-specific code from the core ZIO HTTP module into a dedicated submodule zio-http-netty, completing the modularization goal in issue #3551.

Key Changes

• Created new SBT module: zio-http-netty
• Moved Netty service startup, handlers, and pipeline logic
• Introduced HttpServer trait in core for backend abstraction
• Updated examples to use NettyHttpServer
• Verified sbt compile and sbt test pass

Why

• Supports future backend options
• Keeps zio-http backend-agnostic and lightweight

Bounty

/claim #3551