feat(oci): support both V1 (OciClient) and V2 (OciClientV2) with validation

- Add OciClient back for V1 API (Command R, embeddings)
- OciClientV2 for V2 API (Command A, COHEREV2 format)
- Fail-fast validation: V2 body on V1 client or V1 body on V2 client
  raises ValueError with clear guidance on which client to use
- V1/V2 determined by client class, not body sniffing
- Full V1 chat, stream, and response transforms restored
- Par to par with BedrockClient/BedrockClientV2 architecture
- 47 tests pass (14 integration + 33 unit) against OCI GenAI

Author: fede-kamel

src/cohere/__init__.py

@@ -518,6 +518,7 @@
     "NotFoundError": ".errors",
     "NotImplementedError": ".errors",
     "OAuthAuthorizeResponse": ".types",
+    "OciClient": ".oci_client",
     "OciClientV2": ".oci_client",
     "ParseInfo": ".types",
     "RerankDocument": ".types",
@@ -852,6 +853,7 @@ def __dir__():
     "NotFoundError",
     "NotImplementedError",
     "OAuthAuthorizeResponse",
+    "OciClient",
     "OciClientV2",
     "ParseInfo",
     "RerankDocument",

src/cohere/manually_maintained/lazy_oci_deps.py

@@ -3,7 +3,7 @@
 from typing import Any
 
 OCI_INSTALLATION_MESSAGE = """
-The OCI SDK is required to use OciClientV2.
+The OCI SDK is required to use OciClient or OciClientV2.
 
 Install it with:
     pip install oci