feat(grpc): add support for fetching grades and exams

Implement new gRPC task handlers for retrieving student grades and exam schedules. This includes adding new parser logic for processing score and exam data, and updating the client capabilities to advertise support for these new task types.

- Add `getGrades` and `getExams` handlers in `grpc/handler.go`
- Add `parser/encoding.go`, `parser/exam.go`, and `parser/score.go` for data parsing
- Update `grpc/client.go` to include `TASK_TYPE_GET_GRADES` and `TASK_TYPE_GET_EXAMS` in capabilities

grpc/client.go

@@ -78,6 +78,8 @@ func (c *Client) register() error {
 				Version:  c.version,
 				Capabilities: map[string]string{
 					"TASK_TYPE_GET_SCHEDULE": "true",
+					"TASK_TYPE_GET_GRADES":   "true",
+					"TASK_TYPE_GET_EXAMS":    "true",
 					"TASK_TYPE_LOGIN":        "true",
 				},
 			},