What do you call someone who shoots fireworks professionally?

Pyro is quite simply a shortening of the more ‘proper’ term, which is a pyrotechnician (also sometimes, though more rarely, called a pyrotechnist):

a person who is responsible for the safe storage, handling, and functioning of pyrotechnics and pyrotechnic devices.

Note that pyro can also be (and colloquially is probably more likely to be) a shortened form of pyromaniac, which is someone who likes to set things on fire. If context does not clearly show which you mean, you should always use the full word lest you be misunderstood.

A pyrotechnician :

is a person who is responsible for the safe storage, handling, and functioning of pyrotechnics and pyrotechnic devices. Although the term is generally used in reference to individuals who operate pyrotechnics in the entertainment industry, it can include all individuals who regularly handle explosives. For the purposes of disambiguation, however, individuals who handle more powerful materials for commercial, demolition, or military applications are generally referred to as explosive technicians.

The United States Department of Alcohol, Tobacco, and Firearms, which oversees their licensing in the United States, calls them pyrotechnicians.

The word 'Pyrotechnician' accurately describes the type of professional you are describing, although it has applications outside of the context you've provided. I'm not sure if there is a more specific term available.

Pyrotechnician

Pyrotechnist is the right word, but probably gets about as much use as "fire-worker" in modern context and usage in regard to this particular job. I think you need a background in engineering to be blowing up granite, to make way for a highway. The title is rarely a point of contention in union negotiations by my guess. Good question.