feat(build): split zio-http into multiple modules

Summary

Fixes #3472 /claim #3472

This PR splits the monolithic zio-http artifact into three separate Maven modules as requested in the issue:

New Modules

Module	Description	Platform
`zio-http-core`	Core types (Request, Response, Handler, Routes, Body, Headers, URL, etc.)	JVM + JS
`zio-http-endpoint`	Endpoint API (Endpoint, OpenAPI, gRPC support)	JVM + JS
`zio-http-netty`	Netty-based server/client implementation	JVM only

Benefits

Reduced dependencies: Users who only need core HTTP types don’t need Netty
Better modularity: Clear separation of concerns
Future extensibility: Easier to add alternative backends (HTTP/2, HTTP/3)
Smaller JS bundle: JS users don’t pull in JVM-specific code

Backward Compatibility

The main zio-http module aggregates all three modules, so existing users don’t need to change their dependencies.

Module Dependencies

zio-http-core (no external HTTP deps)
    ↑
zio-http-endpoint (depends on core)
    ↑
zio-http-netty (depends on core + endpoint, adds Netty)
    ↑
zio-http (aggregates all for backward compat)

Mandatory Tasks

I have read and understood the contributing guidelines
I have performed a self-review of my code
The code compiles without warnings
I have added tests that prove my fix is effective or that my feature works (N/A - structural change)
I have updated the documentation accordingly (N/A - no API changes)

Testing

# Compile all modules
sbt compile

# Run tests
sbt test

# Verify module structure
sbt projects

Notes

This is a structural change for milestone 4.0. The actual source files are copied (not moved) to maintain backward compatibility during the transition period. In a follow-up PR, the original files can be removed from zio-http once the new structure is validated.