feat: add NonMaxU32 support via define_nonmax_index_type! macro

[Boshen]

Summary

This PR adds support for creating index types backed by NonMaxU32 from the nonmax crate, enabling memory-efficient Option<Index> representations.

Changes

• ✨ Add nonmax as optional dependency
• 🔧 Extend define_index_type! macro to accept type paths in addition to identifiers
• ✨ Add new define_nonmax_index_type! macro for NonMaxU32-backed indices
• ✅ Add comprehensive tests for NonMaxU32 functionality
• 📝 Update documentation with NonMaxU32 usage examples

Benefits

• Memory efficient: Option<NonMaxIndex> is the same size as NonMaxIndex (4 bytes)
• Type safe: Cannot mix indices from different domains
• Full API compatibility: Supports all standard index operations
• Zero runtime overhead: All operations are inlined

Usage

// Enable the feature in Cargo.toml:
// oxc_index = { version = "3.1", features = ["nonmax"] }

use oxc_index::{IndexVec, define_nonmax_index_type};

define_nonmax_index_type! {
    pub struct StringId;
}

fn main() {
    let mut strings: IndexVec<StringId, String> = oxc_index::index_vec![];
    let id = strings.push("hello".to_string());
    println!("Added at index: {}", id.index());
    
    // Option<StringId> has the same size as StringId (4 bytes)
    assert_eq!(
        std::mem::size_of::<Option<StringId>>(),
        std::mem::size_of::<StringId>()
    );
}

Testing

All tests pass:

• ✅ 37 tests pass with --all-features
• ✅ 35 tests pass without features
• ✅ Documentation builds successfully
• ✅ Library compiles with --no-default-features

Resolves the request to make the macro work with NonMaxU32 from the nonmax crate.

🤖 Generated with Claude Code