notifications: avoid returning after success

[praneelmalapaka]

Summary

The notifications tutorial solution can print Success! and then fault in tcb_consumer at address 0 after returning from main.

This change keeps the consumer alive after printing Success! by yielding in a loop instead of returning from main.

Testing

I reproduced the issue locally with the notifications solution:

cd ~/sel4/sel4-tutorials
mkdir -p notifications_fix_test
cd notifications_fix_test
../init --tut notifications --solution
cd ../notifications_fix_test_build
ninja
./simulate

Before this change, the tutorial reached Success! and then produced a post-success fault similar to:

Success!
Caught cap fault in send phase at address 0
while trying to handle:
vm fault on data at address 0 with status 0x4
in thread ... "tcb_consumer" at address 0

After this change, the tutorial reaches Success! and no longer produces the post-success tcb_consumer fault in my local run.

Notes

This appears related to the existing CI issue where the notifications simulation can reach success but later fail or time out after a tcb_consumer fault.

Related to #100

[lsf37]

Generally, most of the tutorials end with a cap fault, and that is not a problem as such, but you might be right that this relates to #100 because the consumer might reach the fault before the "Success!" print is finished.

Will need to have a closer look.