Missing Azure OpenAI and Ollama providers listed in README

## Description

The README advertises four pluggable providers:

> **Pluggable providers** -- OpenAI (default), Anthropic, Azure OpenAI, Ollama

However, only the OpenAI provider is implemented (`fasteval/providers/openai.py`). There is no implementation for:

- **Azure OpenAI** — no `azure_openai.py` or similar
- **Ollama** — no `ollama.py` or similar

The `create_provider_for_model()` function in `registry.py` also only recognizes `gpt-*`, `o1-*`, `o3-*`, and `claude-*` prefixes.

## Suggested Fix

Either:
1. Implement Azure OpenAI and Ollama providers, or
2. Update the README to reflect the currently available providers and add these as a roadmap/future item