Add scala.reflect.Selectable implementation to AuthHandshaker for Scala 3 compatibility

.devcontainer/README.md

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+# GitHub Codespaces Configuration for Fukuii
+
+This directory contains the configuration for GitHub Codespaces development environment for the Fukuii Ethereum Client.
+
+## What's Included
+
+The devcontainer configuration sets up a complete Scala development environment with:
+
+- **JDK 21** (Temurin distribution) - Required for building Fukuii
+- **SBT 1.5.4+** - Scala Build Tool for compiling and testing
+- **Scala 3.3.4** (LTS) - Primary Scala version used by the project
+- **Metals** - Scala Language Server for VS Code
+- **Git submodules** - Automatically initialized on container creation
+
+## Environment Variables
+
+The following environment variables are pre-configured:
+
+- `FUKUII_DEV=true` - Enables developer-friendly settings (disables fatal warnings, etc.)
+- `JAVA_OPTS` - JVM memory settings optimized for the build process
+
+## Getting Started
+
+1. Open this repository in GitHub Codespaces (click the green "Code" button and select "Open with Codespaces")
+2. Wait for the container to build and initialize (first time may take a few minutes)
+3. Once ready, you can start building:
+
+```bash
+# Compile all modules
+sbt compile-all
+
+# Run tests
+sbt testAll
+
+# Build distribution
+sbt dist
+
+# Format and check code (prepare for PR)
+sbt pp
+```
+
+## VS Code Extensions
+
+The following extensions are automatically installed:
+
+- **Metals** - Scala language support with IntelliSense, refactoring, and more
+- **Scala Syntax** - Syntax highlighting for Scala
+- **TypeScript** - For any TypeScript tooling support
+
+## Cache Directories
+
+The following directories are mounted as volumes to speed up subsequent builds:
+
+- `.ivy2` - Ivy2 dependency cache
+- `.sbt` - SBT cache
+
+These caches persist across container rebuilds, making subsequent builds much faster.
+
+## Troubleshooting
+
+### Metals not working
+
+If the Metals language server doesn't start automatically:
+1. Open the Command Palette (Cmd/Ctrl + Shift + P)
+2. Run "Metals: Import build"
+3. Wait for the import to complete
+
+### Out of Memory Errors
+
+If you encounter OOM errors during build:
+1. The JVM options are already set to use up to 4GB of heap
+2. You may need to increase the Codespace machine size in GitHub settings
+
+### Build Failures
+
+Make sure git submodules are initialized:
+```bash
+git submodule update --init --recursive
+```
+
+## More Information
+
+- [Fukuii Quick Start Guide](../.github/QUICKSTART.md)
+- [Main README](../README.md)
+- [GitHub Codespaces Documentation](https://docs.github.com/en/codespaces)