Add delete model endpoint (DELETE /api/delete)

Implement the Ollama DELETE /api/delete endpoint for removing models
from the server.

- Add DeleteRequest type with model field in src/types/delete.rs
- Add OllamaClient::delete() async method in src/lib.rs
- Register delete module in src/types/mod.rs
- Add usage example in examples/delete.rs

examples/delete.rs

@@ -0,0 +1,16 @@
+use std::{env, error::Error};
+
+use ollama_rs::OllamaClient;
+use ollama_rs::types::delete::DeleteRequest;
+
+#[tokio::main]
+async fn main() -> Result<(), Box<dyn Error>> {
+    tracing_subscriber::fmt().init();
+    let _ = dotenvy::dotenv();
+    let server_address = env::var("OLLAMA_SERVER")?;
+    let model = env::args().nth(1).expect("usage: delete <model>");
+    let ollama_client = OllamaClient::new(server_address);
+    ollama_client.delete(DeleteRequest::new(&model)).await?;
+    println!("Model '{}' deleted successfully", model);
+    Ok(())
+}