fix: OCI tool use returns 400 — tool type field not uppercased

[fede-kamel]

Bug

OciClientV2.chat() with tools parameter returns a 400 error from OCI Generative AI:

status_code: 400, body: {'message': 'Please pass in correct format of request.'}

Root Cause

OCI Generative AI expects all enum fields uppercased. The SDK already transforms message roles ("user" → "USER") and content types ("text" → "TEXT"), but passes the tool type field through as-is ("function" instead of "FUNCTION").

Reproduction

import cohere

client = cohere.OciClientV2(
    oci_region="us-chicago-1",
    oci_compartment_id="ocid1.compartment.oc1...",
)

# This returns 400
response = client.chat(
    model="command-a-03-2025",
    messages=[{"role": "user", "content": "What's the weather in Toronto?"}],
    tools=[{
        "type": "function",
        "function": {
            "name": "get_weather",
            "description": "Get current weather",
            "parameters": {"type": "object", "properties": {"location": {"type": "string"}}, "required": ["location"]},
        },
    }],
)

Expected

Tool use works — OCI returns finish_reason=TOOL_CALL with tool_calls.

Impact

All tool use via OciClientV2 is broken on OCI on-demand inference.