docs(inference): fix unstable internal import in reranking how-to

## Purpose

The "Using the RerankModel enum" code snippet imported `Inference` from
`pinecone.client.inference`, an internal module path not in the public
API. Teaching users to import from internal paths violates the
api-stability contract and will break if the module is reorganized.

## Solution

Replaced `from pinecone.client.inference import Inference` +
`Inference.RerankModel.Bge_Reranker_V2_M3` with the stable top-level
import `from pinecone import Pinecone, RerankModel` and the direct
`RerankModel.Bge_Reranker_V2_M3` reference. `RerankModel` is exported
from `pinecone.__all__` and `_LAZY_IMPORTS`, making it part of the
stable public API.

Author: jhamon

docs/how-to/inference/reranking.md

@@ -88,13 +88,12 @@ Use the {class}`~pinecone.models.enums.RerankModel` enum for tab-completion and
 safety:
 
 ```python
-from pinecone import Pinecone
-from pinecone.client.inference import Inference
+from pinecone import Pinecone, RerankModel
 
 pc = Pinecone(api_key="your-api-key")
 
 result = pc.inference.rerank(
-    model=Inference.RerankModel.Bge_Reranker_V2_M3,
+    model=RerankModel.Bge_Reranker_V2_M3,
     query="machine learning",
     documents=documents,
 )