[Zig] Implement BlockStream module

[roninjin10]

Summary

Implement BlockStream module in Zig for block fetching and streaming.

TS Functions to Port

• fetchBlock - Fetch block by number
• fetchBlockByHash - Fetch block by hash
• fetchBlockReceipts - Fetch receipts for block
• toLightBlock - Convert to lightweight block
• Retry logic with exponential backoff
• Streaming/subscription support

Features

• Block range fetching
• Reorg detection
• Backfill support
• Error handling for RPC failures

Current State

Module missing entirely in Zig.

Note

This is a higher-level abstraction. May depend on JSON-RPC client implementation.

Note: Issue created by Claude AI assistant, not @roninjin10 or @fucory