[fix] remove useless panics

[avelex]

The main goal of PR is to remove unnecessary panic where it should not be.

For example:

msg, err := message.ToMessage()
if err != nil {
	panic(err)
}

So If such code is placed in a function which does not mean panic is present, unpleasant things may happen in the future. This is why panics have been removed from the statefunContext and storage module.

Also, the prefix Must has been added to functions that must be completed and cannot be avoided in the future

[tbal999]

makes sense to me what you have done

[pocockn]

LGTM

[avelex]

https://issues.apache.org/jira/browse/FLINK-31456