Add "collapse by default" setting

Currently, test blocks are always collapsed by default (unless they're the top most call expression in a file).

This should be controlled by an exposed setting, that users can control.

Locate the code that currently decides when test blocks are collapsed, then trace how IntelliJ plugin settings are exposed. Define the setting's default to preserve current behavior and verify that changing it controls the folding behavior described in the issue.

Written by the indexing model from the issue text.