Add scope-specific test params

[alin23]

Motivation

Some testing libraries need params/switches to run a specific test.
For example, Specter:

• needs --select-module for the Run current file tests command
• needs --select-tests for the Run current test command

Also Python's unittest needs a -s switch to run a specific test.

Solution

Add test_params setting as a dict where you can specify params for all three testing commands.