feat: add visualization for repeated routines

[mstechly]

Description

Adds visualization to QREF subroutine with repetitions.

It looks like this:

Code for repro (from qref/tests/qref/data/valid_programs directory):

import yaml
import glob
from qref.experimental.rendering import to_graphviz
paths = glob.glob("programs_with_repetitions/*")
valid_programs = []
for path in paths:
    with open(path) as f:
        data = yaml.safe_load(f)
        valid_programs.append(data["input"])
to_graphviz(valid_programs[0])

Please verify that you have completed the following steps

• I have self-reviewed my code.
• I have included test cases validating introduced feature/fix. (NA)
• I have updated documentation. (NA)