[BUG] LightevalTaskConfig doesn't support comparison, but Cache management uses sorted on it

## Describe the bug
Specify two tasks as below:
helm|boolq|0
helm|boolq:contrastset|0
The current logic will assume "helm|boolq" is a group and will add "helm|boolq:contrastset" again, then "helm|boolq:contrastset" will appear twice, later at SampleCache:_get_task_hash sorted is used to sort these two, and
an error "<" is not supported on LightevalTaskConfig is raised

## To Reproduce
Specify two tasks as below in yaml:
helm|boolq|0
helm|boolq:contrastset|0

## Expected behavior
Run should succeed

## Version info
0.11.0