Improve docstrings for result APIs

### Description of the modifications

Add Examples in the docstrings of result APIs, like what was done in `ModalMechanicalSimulation.displacement()`.

Do one specific for `stress` to illustrate `location`, then refer to those in the other result types.

### Useful links and references

_No response_

Start with the existing examples in ModalMechanicalSimulation.displacement() and inspect the docstrings for the result APIs. Add a specific stress example showing location, then use it as the reference for examples in the other result types. Done means the result API docstrings consistently include these examples.

Written by the indexing model from the issue text.