feat: implement auto-refresh capability for Linear and Notion connectors similar to google oauth based ones

- Enhanced LinearConnector and NotionHistoryConnector classes to support automatic token refresh, improving reliability in accessing APIs.
- Updated initialization to require session and connector ID, allowing for dynamic credential management.
- Introduced new credential schemas for Linear and Notion, encapsulating access and refresh tokens with expiration handling.
- Refactored indexers to utilize the new connector structure, ensuring seamless integration with the updated authentication flow.
- Improved error handling and logging during token refresh processes for better debugging and user feedback.

surfsense_backend/app/schemas/linear_auth_credentials.py

@@ -0,0 +1,66 @@
+from datetime import UTC, datetime
+
+from pydantic import BaseModel, field_validator
+
+
+class LinearAuthCredentialsBase(BaseModel):
+    access_token: str
+    refresh_token: str | None = None
+    token_type: str = "Bearer"
+    expires_in: int | None = None
+    expires_at: datetime | None = None
+    scope: str | None = None
+
+    @property
+    def is_expired(self) -> bool:
+        """Check if the credentials have expired."""
+        if self.expires_at is None:
+            return False
+        return self.expires_at <= datetime.now(UTC)
+
+    @property
+    def is_refreshable(self) -> bool:
+        """Check if the credentials can be refreshed."""
+        return self.refresh_token is not None
+
+    def to_dict(self) -> dict:
+        """Convert credentials to dictionary for storage."""
+        return {
+            "access_token": self.access_token,
+            "refresh_token": self.refresh_token,
+            "token_type": self.token_type,
+            "expires_in": self.expires_in,
+            "expires_at": self.expires_at.isoformat() if self.expires_at else None,
+            "scope": self.scope,
+        }
+
+    @classmethod
+    def from_dict(cls, data: dict) -> "LinearAuthCredentialsBase":
+        """Create credentials from dictionary."""
+        expires_at = None
+        if data.get("expires_at"):
+            expires_at = datetime.fromisoformat(data["expires_at"])
+
+        return cls(
+            access_token=data["access_token"],
+            refresh_token=data.get("refresh_token"),
+            token_type=data.get("token_type", "Bearer"),
+            expires_in=data.get("expires_in"),
+            expires_at=expires_at,
+            scope=data.get("scope"),
+        )
+
+    @field_validator("expires_at", mode="before")
+    @classmethod
+    def ensure_aware_utc(cls, v):
+        # Strings like "2025-08-26T14:46:57.367184"
+        if isinstance(v, str):
+            # add +00:00 if missing tz info
+            if v.endswith("Z"):
+                return datetime.fromisoformat(v.replace("Z", "+00:00"))
+            dt = datetime.fromisoformat(v)
+            return dt if dt.tzinfo else dt.replace(tzinfo=UTC)
+        # datetime objects
+        if isinstance(v, datetime):
+            return v if v.tzinfo else v.replace(tzinfo=UTC)
+        return v