### Check for existing issues

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

### The Feature

Add an optional, capability-based SDK interface for proactively querying quota or balance information reported by an upstream provider. This should be distinct from LiteLLM's configured budgets and spend observed by the proxy.

A possible interface:

```python snapshot = await litellm.aprobe_provider_quota( model=model, api_key=api_key, api_base=api_base, ) ```

with a normalized result along these lines:

```python ProviderQuotaSnapshot( provider="openrouter", scope="credential", # credential/account/project/subscription unit="usd", # usd/tokens/requests/percent limit=25.0, used=6.5, remaining=18.5, resets_at=None, as_of=..., ) ```

Suggested implementation:

- Add an optional `probe_quota` capability to provider configurations; unsupported providers return `None` or a typed `NotSupported` result. - Reuse LiteLLM's provider resolution and credential handling rather than requiring callers to detect providers. - Implement adapters only where providers expose a supported API, potentiall…