feat: support per-protocol encoding in reqresp v1

[samcm]

Summary

This PR improves the reqresp v1 package to support per-protocol encoding/compression instead of global configuration. This provides much better flexibility and matches real-world usage patterns.

Problem

The original design forced all protocols to use the same encoder/compressor configured at the service level. This is too restrictive because:

• Consensus protocols typically use SSZ encoding
• Metadata protocols might use JSON
• Some protocols need compression (Snappy), others don't
• Different protocols have different performance/size tradeoffs

Solution

• Remove global encoder/compressor from ServiceConfig
• Add encoder/compressor to HandlerOptions for per-protocol configuration
• Add SendRequestWithOptions to allow per-request encoding on client side
• Update examples to demonstrate protocol-specific encoding

Key Changes

1. Handler Registration: Now requires HandlerOptions with encoder

opts := v1.HandlerOptions{
    Encoder:    JSONEncoder{},     // or SSZEncoder{} 
    Compressor: SnappyCompressor{}, // or nil
    RequestTimeout: 30 * time.Second,
}
v1.RegisterProtocol(service, protocol, handler, opts)

2. Client Requests: Use SendRequestWithOptions for encoding

reqOpts := v1.RequestOptions{
    Encoder:    JSONEncoder{},  // Must match server
    Compressor: nil,
    Timeout:    5 * time.Second,
}
service.SendRequestWithOptions(ctx, peer, proto, req, &resp, reqOpts)

3. Improved Examples:
   • Middleware example now shows actual handler wrapping
   • Comments indicate where different encoders would be used

Breaking Changes

• RegisterProtocol and RegisterChunkedProtocol now require HandlerOptions parameter
• ClientConfig no longer has Encoder/Compressor fields
• Service constructor no longer validates encoder presence

Test Plan

• Package compiles successfully
• Examples compile and demonstrate usage
• Unit tests to be added (tracked separately)

🤖 Generated with Claude Code

[mattevans]

Very nice 🎖️