Callgrind inputs: Some called functions along with their callees are detached from the rest of execution at the root level

When visualizing the Callgrind output, some functions appear on the root level, while being called by other functions in the Callgrind file (they appear as `cfn` callees in other functions in the Callgrind output).

The example output for Callgrind ([download link](https://raw.githubusercontent.com/antmicro/openroad-callgrind-report/main/docs/_static/speedscope/callgrind/ariane/992185_5_1_grt_callgrind.out)):


Other visualizations demonstrating the issue:



The expected behavior is to have those methods embedded in the main call graph, not separately, starting from the root level.