Add public telemetry tracer helper

[rbarbadillo]

Summary

• add get_telemetry_tracer(client, name=None) to mistralai.extra.observability
• select the client custom/dedicated/global telemetry provider without exposing provider lifecycle management
• cover dedicated, global, custom provider, and disabled telemetry behavior

Usage

from mistralai.client import Mistral
from mistralai.extra.observability import configure_telemetry, get_telemetry_tracer

client = Mistral(api_key="your-api-key")
configure_telemetry(client)

tracer = get_telemetry_tracer(client, "my-agent")

with tracer.start_as_current_span("invoke_agent"):
    response = client.chat.complete(
        model="mistral-large-latest",
        messages=[{"role": "user", "content": "Find recent AI news."}],
    )

    with tracer.start_as_current_span("execute_tool web_search") as tool_span:
        tool_span.set_attribute("gen_ai.tool.name", "web_search")
        tool_span.set_attribute("gen_ai.tool.type", "function")
        search_results = web_search(response)
        tool_span.set_attribute("gen_ai.tool.call.result", str(search_results))