### Check for existing issues

- [x] I have searched the existing issues and checked that my issue is not a duplicate.

### What happened?

### Bug Description

When using the LiteLLM proxy with multiple deployments of the same model across different Ollama hosts, failover to a healthy deployment never occurs when a host is unreachable. The router retries the same dead host repeatedly until `num_retries` is exhausted, then returns an error — even though other healthy deployments exist in the same model group.

### Root Cause

In `litellm/router_utils/cooldown_handlers.py`, the `_is_cooldown_required()` function contains a hardcoded exclusion list:

```python # line 57 ignored_strings = ["APIConnectionError"] ```

This causes `_is_cooldown_required()` to return `False` for any exception containing `"APIConnectionError"` in its string representation, regardless of `allowed_fails` or `allowed_fails_policy` configuration. As a result:

- The failed deployment is never added to the cooldown set - `async_get_available_deployment` continues to select the same dead host on every retry - All configured retries are wasted against the same unreachable host - No failover occurs

This is confir…