docs: add comprehensive component documentation

[shentongmartin]

Summary

This PR adds comprehensive component documentation for all 64 component implementations in the eino-ext project.

Changes

1. New File: components.md

• Created detailed documentation for all 64 components across 8 categories
• Organized in table format with columns: Name, Import Path, Description, Key Features, GitHub URL
• Categories include:
  • ChatModel (10 implementations)
  • Embedding (8 implementations)
  • Indexer (10 implementations)
  • Retriever (12 implementations)
  • Tool (10 implementations)
  • Prompt (2 implementations)
  • Document (12 implementations: loaders, parsers, transformers)
  • Callback Handlers (4 implementations)

2. Updated README.md

• Replaced simple component list with comprehensive Component Summary table
• Added component counts for each category
• Listed all implementations with proper names
• Added prominent link to components.md for detailed information
• Removed redundant callback handlers bullet point

3. Updated README.zh_CN.md

• Added 组件概览 (Component Overview) section with Chinese translations
• Same comprehensive table structure as English version
• Added link to components.md with Chinese description
• Removed redundant callback handlers bullet point

Benefits

• Better discoverability: Users can quickly find all available components
• Comprehensive information: Each component includes import path, description, features, and GitHub link
• Easy to scan: Table format makes it simple to compare and find components
• Bilingual support: Both English and Chinese documentation updated~