docs: update README and examples for v1.0.0

- Rewrite README with all new endpoints and current model names
- Add available models table with constructors
- Add FIM and OCR examples
- Update all examples for string-based Model type
- Update streaming example for Option<String> delta content
- Use serde_json::json!() for tool schemas in examples
- Add .envrc to .gitignore

examples/fim.rs

@@ -0,0 +1,21 @@
+use mistralai_client::v1::{
+    client::Client,
+    constants::Model,
+    fim::FimParams,
+};
+
+fn main() {
+    // This example suppose you have set the `MISTRAL_API_KEY` environment variable.
+    let client = Client::new(None, None, None, None).unwrap();
+
+    let model = Model::codestral_latest();
+    let prompt = "def fibonacci(n):".to_string();
+    let options = FimParams {
+        suffix: Some("\n    return result".to_string()),
+        temperature: Some(0.0),
+        ..Default::default()
+    };
+
+    let response = client.fim(model, prompt, Some(options)).unwrap();
+    println!("Completion: {}", response.choices[0].message.content);
+}