feat(config): add per-auth disable_cooling override support

- Introduced `disable_cooling` metadata field for fine-grained control over cooldown scheduling.
- Updated `Auth` object to include `Metadata` with conditional logic for handling empty states.
- Added YAML configuration support for `disable_cooling` in API key definitions across providers.
- Enhanced unit tests to validate `disable_cooling` behavior in various scenarios.

config.example.yaml

@@ -157,6 +157,7 @@ nonstream-keepalive-interval: 0
 # gemini-api-key:
 #   - api-key: "AIzaSy...01"
 #     prefix: "test" # optional: require calls like "test/gemini-3-pro-preview" to target this credential
+#     disable-cooling: false # optional: per-auth override for auth/model cooldown scheduling
 #     base-url: "https://generativelanguage.googleapis.com"
 #     headers:
 #       X-Custom-Header: "custom-value"
@@ -176,6 +177,7 @@ nonstream-keepalive-interval: 0
 # codex-api-key:
 #   - api-key: "sk-atSM..."
 #     prefix: "test" # optional: require calls like "test/gpt-5-codex" to target this credential
+#     disable-cooling: false # optional: per-auth override for auth/model cooldown scheduling
 #     base-url: "https://www.example.com" # use the custom codex API endpoint
 #     headers:
 #       X-Custom-Header: "custom-value"
@@ -195,6 +197,7 @@ nonstream-keepalive-interval: 0
 #   - api-key: "sk-atSM..." # use the official claude API key, no need to set the base url
 #   - api-key: "sk-atSM..."
 #     prefix: "test" # optional: require calls like "test/claude-sonnet-latest" to target this credential
+#     disable-cooling: false # optional: per-auth override for auth/model cooldown scheduling
 #     base-url: "https://www.example.com" # use the custom claude API endpoint
 #     headers:
 #       X-Custom-Header: "custom-value"
@@ -250,6 +253,7 @@ nonstream-keepalive-interval: 0
 #     disabled: false # optional: set to true to disable this provider without removing it
 #     prefix: "test" # optional: require calls like "test/kimi-k2" to target this provider's credentials
 #     base-url: "https://openrouter.ai/api/v1" # The base URL of the provider.
+#     disable-cooling: false # optional: per-provider override for auth/model cooldown scheduling
 #     headers:
 #       X-Custom-Header: "custom-value"
 #     api-key-entries: