Merge #904

904: Support "Hybrid" parameter in `IndexSearchRequest` to enable multi search with hybrid search r=curquiza a=ErrorProne

# Pull Request

## Related issue
- 

## What does this PR do?
- Adds the Hybrid search option to IndexSearchRequest which is used in multi [search queries](https://www.meilisearch.com/docs/reference/api/multi_search) 
- This is basically a clone of the hybrid implementation in the SearchRequest class

## PR checklist
Please check if your PR fulfills the following requirements:
- [ ] Does this PR fix an existing issue, or have you listed the changes applied in the PR description (and why they are needed)?
- [ ] Have you read the contributing guidelines?
- [x] Have you made sure that the title is accurate and descriptive of the changes?

Thank you so much for contributing to Meilisearch!


<!-- This is an auto-generated comment: release notes by coderabbit.ai -->
## Summary by CodeRabbit

* **New Features**
  * Added hybrid search configuration to requests, allowing users to provide semantic ratio and embedder settings for combined keyword + semantic search; hybrid settings are included in request serialization.

* **Tests**
  * Added tests verifying hybrid configuration is correctly represented in serialized request output and stringified form across multiple parameter combinations.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Co-authored-by: fherpich <finn@thebuilders.de>

Author: meili-bors[bot]

src/main/java/com/meilisearch/sdk/IndexSearchRequest.java

@@ -1,5 +1,6 @@
 package com.meilisearch.sdk;
 
+import com.meilisearch.sdk.model.Hybrid;
 import com.meilisearch.sdk.model.MatchingStrategy;
 import lombok.*;
 import lombok.experimental.Accessors;
@@ -38,14 +39,15 @@ public class IndexSearchRequest {
     private FederationOptions federationOptions;
     protected String[] locales;
     protected String distinct;
+    protected Hybrid hybrid;
     protected Boolean retrieveVectors;
 
     /**
      * Constructor for MultiSearchRequest for building search queries with the default values:
      * offset: 0, limit: 20, attributesToRetrieve: ["*"], attributesToCrop: null, cropLength: 200,
      * attributesToHighlight: null, filter: null, showMatchesPosition: false, facets: null, sort:
      * null, showRankingScore: false, showRankingScoreDetails: false, rankingScoreThreshold: null
-     * distinct: null, retrieveVectors: false
+     * distinct: null, retrieveVectors: false, hybrid: null
      *
      * @param indexUid uid of the requested index String
      */
@@ -108,7 +110,8 @@ public String toString() {
                         .putOpt("attributesToSearchOn", this.attributesToSearchOn)
                         .putOpt("locales", this.locales)
                         .putOpt("distinct", this.distinct)
-                        .putOpt("retrieveVectors", this.retrieveVectors);
+                        .putOpt("retrieveVectors", this.retrieveVectors)
+                        .putOpt("hybrid", this.hybrid != null ? this.hybrid.toJSONObject() : null);
 
         return jsonObject.toString();
     }

src/test/java/com/meilisearch/sdk/IndexSearchRequestTest.java

@@ -0,0 +1,57 @@
+package com.meilisearch.sdk;
+
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.Matchers.equalTo;
+import static org.hamcrest.Matchers.is;
+
+import com.meilisearch.sdk.model.Hybrid;
+import org.junit.jupiter.api.Test;
+
+class IndexSearchRequestTest {
+    @Test
+    void toStringWithHybridUsingBuilder() {
+        IndexSearchRequest classToTest =
+                IndexSearchRequest.builder()
+                        .q("This is a Test")
+                        .hybrid(Hybrid.builder().semanticRatio(0.5).embedder("default").build())
+                        .build();
+
+        String expected =
+                "{\"q\":\"This is a Test\",\"hybrid\":{\"semanticRatio\":0.5,\"embedder\":\"default\"}}";
+        assertThat(classToTest.toString(), is(equalTo(expected)));
+
+        // Verify getters
+        assertThat(classToTest.getHybrid().getSemanticRatio(), is(equalTo(0.5)));
+        assertThat(classToTest.getHybrid().getEmbedder(), is(equalTo("default")));
+    }
+
+    @Test
+    void toStringWithHybridAndOtherParameters() {
+        IndexSearchRequest classToTest =
+                IndexSearchRequest.builder()
+                        .q("This is a Test")
+                        .offset(200)
+                        .limit(900)
+                        .hybrid(
+                                Hybrid.builder()
+                                        .semanticRatio(0.7)
+                                        .embedder("custom-embedder")
+                                        .build())
+                        .build();
+
+        String expected =
+                "{\"q\":\"This is a Test\",\"hybrid\":{\"semanticRatio\":0.7,\"embedder\":\"custom-embedder\"},\"offset\":200,\"limit\":900}";
+        assertThat(classToTest.toString(), is(equalTo(expected)));
+    }
+
+    @Test
+    void toStringWithHybridOnlyEmbedder() {
+        IndexSearchRequest classToTest =
+                new IndexSearchRequest("someIndexUuid")
+                        .setQuery("This is a Test")
+                        .setHybrid(Hybrid.builder().embedder("default").build());
+
+        String expected = "{\"q\":\"This is a Test\",\"hybrid\":{\"embedder\":\"default\"}}";
+        assertThat(classToTest.toString(), is(equalTo(expected)));
+    }
+}