fix(python): Update to latest cohere reranking api (#1212)

Fixes https://github.com/lancedb/lancedb/issues/1196
Cohere introduced a breaking change in their reranker API starting
version 5.0.0. More context in discussion here
https://github.com/cohere-ai/cohere-python/issues/446

python/python/lancedb/rerankers/cohere.py

@@ -1,4 +1,5 @@
 import os
+import semver
 from functools import cached_property
 from typing import Union
 
@@ -42,6 +43,14 @@ class CohereReranker(Reranker):
     @cached_property
     def _client(self):
         cohere = attempt_import_or_raise("cohere")
+        # ensure version is at least 0.5.0
+        if (
+            hasattr(cohere, "__version__")
+            and semver.compare(cohere.__version__, "5.0.0") < 0
+        ):
+            raise ValueError(
+                f"cohere version must be at least 0.5.0, found {cohere.__version__}"
+            )
         if os.environ.get("COHERE_API_KEY") is None and self.api_key is None:
             raise ValueError(
                 "COHERE_API_KEY not set. Either set it in your environment or \
@@ -51,11 +60,14 @@ class CohereReranker(Reranker):
 
     def _rerank(self, result_set: pa.Table, query: str):
         docs = result_set[self.column].to_pylist()
-        results = self._client.rerank(
+        response = self._client.rerank(
             query=query,
             documents=docs,
             top_n=self.top_n,
             model=self.model_name,
+        )
+        results = (
+            response.results
         )  # returns list (text, idx, relevance) attributes sorted descending by score
         indices, scores = list(
             zip(*[(result.index, result.relevance_score) for result in results])