launch_mechanical has a version argument that is only supported if pypim is configured

it should be usable without pypim.

Furthermore, pim should only be installed using a [pim] option.

`pip install ansys-mechanical-core` => pim not installed

`pip install ansys-mechanical-core[pim]` => pim installed

Start at the launch_mechanical entry point and inspect how its version argument depends on pypim, along with the package dependency configuration. Verify both installation commands: the base package should omit pim, while the [pim] extra should install it, and launch_mechanical should remain usable without pypim.

Written by the indexing model from the issue text.