Pull out updateAstAndFocus in order to make unit tests for applyFilletToSelection

[max-mrgrsk]

This issue is part of the larger Fillet UI (#2606) project.

Currently, the updateAstAndFocus function is invoked directly within the main function applyFilletToSelection , which causes challenges when running unit tests. Specifically, the kclManager.updateAst command is not compatible with our current unit test setup.

To resolve this, we need to refactor the code and pull the updateAstAndFocus function out of the main flow. This will allow us to properly test the core functionality. Which is needed for upcoming multiple selection tests.