feat: Add incremental delivery support for Relay connections

[jwaldrip]

Absinthe Relay Incremental Delivery

Relay connection support for GraphQL @defer and @stream directives.

Overview

This package extends absinthe_relay to support incremental delivery with Relay-style connections. Stream edges incrementally while maintaining cursor consistency and proper connection structure throughout the streaming process.

Features

• ✅ Relay Specification: Full compliance with Relay Cursor Connection spec
• ✅ Cursor Consistency: Maintains proper cursor ordering during streaming
• ✅ Connection Structure: Preserves pageInfo and connection metadata
• ✅ Bidirectional Pagination: Supports forward and backward streaming
• ✅ Error Resilience: Graceful handling of partial failures

Installation

This functionality is included when using both absinthe_relay and incremental delivery:

def deps do
  [
    {:absinthe, "~> 1.8"},
    {:absinthe_relay, "~> 1.5"}
  ]
end

Basic Usage

Schema Definition

defmodule MyApp.Schema do
  use Absinthe.Schema
  use Absinthe.Relay.Schema, :modern
  
  import_types Absinthe.Type.BuiltIns
  
  connection node_type: :post
  connection node_type: :user
  
  query do
    connection field :posts, node_type: :post do
      arg :category, :string
      
      resolve fn args, _ ->
        # Your existing connection resolver
        MyApp.Resolvers.list_posts(args)

## ⚠️ DEPENDENCY NOTICE
**This PR depends on absinthe-graphql/absinthe#1377**  
The main absinthe package must be merged first before this PR can be merged.

## Features
- Stream edges incrementally while maintaining cursor consistency
- Compatible with forward and backward pagination
- Maintains proper connection structure during streaming
- Preserves pageInfo accuracy throughout streaming

## Implementation
- `Absinthe.Relay.Incremental.Connection` - Streaming connection support
- Cursor consistency management
- Edge batching for efficient delivery

## Testing
- Pagination consistency tests
- Cursor ordering validation
- Connection structure integrity

## Breaking Changes
None - incremental delivery is opt-in and backward compatible.

🤖 Generated with Claude Code

[jwaldrip]

Checking in on this clean version of the incremental delivery support for Relay connections. This is a companion to absinthe#1377. Any feedback?