feat: Add native Cloudflare D1 database driver support

[hongkongkiwi]

Summary

Add a native D1 driver for Sea-ORM that enables seamless integration with Cloudflare Workers D1 databases.

Key Features

• D1Connector & D1Connection: Types wrapping worker::D1 binding
• Full SQL execution: Support for execute, query_one, query_all
• D1QueryExecutor trait: Entity query support (works around wasm-bindgen Send bound limitation)
• D1Row & D1ExecResult: Result types for D1 query handling
• TryGetable support: D1-specific type conversions

Example Usage

use worker::{Env, event};

#[event(fetch)]
async fn fetch(req: Request, env: Env, _ctx: Context) -> Result<Response> {
    let d1 = env.d1("DB")?;
    let db = sea_orm::Database::connect_d1(d1).await?;
    
    // Entity queries work!
    let cakes = cake::Entity::find().all(&db).await?;
    
    // Direct SQL also works
    db.execute(statement).await?;
    
    Ok(Response::ok("Hello")?)
}

Technical Notes

The implementation uses a custom D1QueryExecutor trait with impl Future return type to work around wasm-bindgen's requirement that futures be Send. This allows Entity queries without requiring the full ConnectionTrait implementation.

Files Changed

• src/driver/d1.rs: Core D1 driver implementation
• src/driver/mod.rs: Module exports
• src/database/db_connection.rs: Connection type integration
• src/database/mod.rs: connect_d1 API
• src/executor/query.rs: TryGetable support for D1 types
• examples/d1_example/: Complete working example

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