refactor(oci): drop V1 OciClient, go V2-only

- Remove OciClient (V1 API) class entirely
- Remove all is_v2 parameter threading and body-sniffing detection
- Remove V1 chat (single message string), V1 stream format, generate/rerank endpoints
- OciClientV2 is now the only client, always uses COHEREV2 apiFormat
- Add validation: raise ValueError if messages array is missing
- Add oci_client.py to .fernignore to survive Fern regeneration
- Update __init__.py and lazy_oci_deps.py to reference only OciClientV2
- Update tests: remove V1 test classes, add missing-messages test
- All 41 tests pass (11 integration + 30 unit) against LUIGI_FRA_API

Author: fede-kamel

.fernignore

@@ -15,6 +15,7 @@ src/cohere/manually_maintained/__init__.py
 src/cohere/bedrock_client.py
 src/cohere/aws_client.py
 src/cohere/sagemaker_client.py
+src/cohere/oci_client.py
 src/cohere/client_v2.py
 mypy.ini
 src/cohere/aliases.py

src/cohere/__init__.py

@@ -518,7 +518,6 @@
     "NotFoundError": ".errors",
     "NotImplementedError": ".errors",
     "OAuthAuthorizeResponse": ".types",
-    "OciClient": ".oci_client",
     "OciClientV2": ".oci_client",
     "ParseInfo": ".types",
     "RerankDocument": ".types",
@@ -853,7 +852,6 @@ 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 OciClient or OciClientV2.
+The OCI SDK is required to use OciClientV2.
 
 Install it with:
     pip install oci