Extension: Basic crate search via crates.io API

[nikomatsakis]

Overview

Add ability to search for crates on crates.io using text-based queries, complementing the existing example search functionality.

Proposed API

// Search by keywords, description, etc.
let crates = Eg::search_crates("web framework").await?;
let crates = Eg::search_crates("async http client").await?;

// Browse by category
let crates = Eg::browse_category("web-programming").await?;

// Combined workflow: discover crates, then search examples
let web_frameworks = Eg::search_crates("web framework").await?;
for crate_info in web_frameworks.iter().take(5) {
    let examples = Eg::rust_crate(&crate_info.name)
        .pattern(r"route")?
        .search().await?;
}

Implementation

• Use existing crates_io_api dependency
• Add search endpoints: /api/v1/crates with query parameters
• Return structured CrateInfo with name, description, downloads, etc.
• Integrate with existing builder pattern

Benefits

• Crate discovery: Find relevant crates before diving into examples
• LLM workflow: "Find HTTP clients, then show me retry examples"
• Exploration: Browse categories and popular crates
• Foundation: Sets up infrastructure for more advanced search features

Acceptance Criteria

• Text-based crate search with keyword matching
• Category browsing support
• Structured results with crate metadata
• Integration with existing example search workflow
• Comprehensive error handling for API failures

Out of Scope

• Semantic/embedding-based search (separate issue)
• Local caching of crate metadata
• Advanced filtering/sorting options