Update to latest Mistral AI API (v1.0.0)

- Replace closed Model enum with flexible string-based Model type
  with constructor methods for all current models (Mistral Large 3,
  Small 4, Magistral, Codestral, Devstral, Pixtral, Voxtral, etc.)
- Add new API endpoints: FIM completions, Files, Fine-tuning, Batch
  jobs, OCR, Audio transcription, Moderations/Classifications, and
  Agent completions (sync + async for all)
- Add new chat fields: frequency_penalty, presence_penalty, stop,
  n, parallel_tool_calls, reasoning_effort, min_tokens, json_schema
  response format
- Add embedding fields: output_dimension, output_dtype
- Tool parameters now accept raw JSON Schema (serde_json::Value)
  instead of limited enum types
- Add tool call IDs and Required tool choice variant
- Add DELETE HTTP method support and multipart file upload
- Bump thiserror to v2, add reqwest multipart feature
- Remove strum dependency (no longer needed)
- Update all tests and examples for new API

examples/ocr.rs

@@ -0,0 +1,25 @@
+use mistralai_client::v1::{
+    client::Client,
+    constants::Model,
+    ocr::{OcrDocument, OcrRequest},
+};
+
+fn main() {
+    // This example suppose you have set the `MISTRAL_API_KEY` environment variable.
+    let client = Client::new(None, None, None, None).unwrap();
+
+    let request = OcrRequest {
+        model: Model::mistral_ocr_latest(),
+        document: OcrDocument::from_url("https://arxiv.org/pdf/2201.04234"),
+        pages: Some(vec![0]),
+        table_format: None,
+        include_image_base64: None,
+        image_limit: None,
+    };
+
+    let response = client.ocr(&request).unwrap();
+    for page in &response.pages {
+        println!("--- Page {} ---", page.index);
+        println!("{}", &page.markdown[..200.min(page.markdown.len())]);
+    }
+}