### Check for existing issues

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

### What happened?

Per-model spend counters include the model and duration, but their budget-window start keys do not on current `litellm_internal_staging` at commit `65ca095d4d15a82372e53a547a2390a69f7e1797`

[`async_log_success_event`](https://github.com/BerriAI/litellm/blob/65ca095d4d15a82372e53a547a2390a69f7e1797/litellm/proxy/hooks/model_max_budget_limiter.py#L270-L323) builds these spend keys:

```text virtual_key_spend:{virtual_key}:{model}:{budget_duration} end_user_model_spend:{end_user_id}:{model}:{budget_duration} ```

It builds these start keys:

```text virtual_key_budget_start_time:{virtual_key} end_user_budget_start_time:{end_user_id} ```

The model and duration are absent from the start key

[`_increment_spend_for_key`](https://github.com/BerriAI/litellm/blob/65ca095d4d15a82372e53a547a2390a69f7e1797/litellm/router_strategy/budget_limiter.py#L455-L495) reads that shared timestamp, compares it with the current model's `budget_duration`, and resets the current spend key plus the shared start key when the current duration is expired

Two models configu…