analysis/tasks: Create an explicitly human readable df_task_states

Created by: valschneider

The current df_task_states forces the user to use the

df[df.curr_state == TaskState.TASK_*.char]

pattern since we store the state's character into the dataframe to be readable. Analysis code shouldn't have to deal with this, and using pure ints will make filtering a bit faster.

Change the existing df_task_states to use pure ints, and add a stringified sibling that uses the char representation of TaskState.