chore: remove pyvista dependency constraint from pyproject.toml

[germa89]

Description

As the title

Issue linked

Related to #4158, #4166

Checklist

• I have visited and read Develop PyMAPDL.
• I have tested my changes locally
• I have added necessary documentation or updated existing documentation.
• I have followed the PyMAPDL coding style guidelines.
• I have added appropriate unit tests that also ensure the minimal coverage criteria.
• I have reviewed my changes before submitting this pull request.
• I have linked the issue or issues that are solved to the PR if any.
• I have assigned this PR to myself.
• I have marked this PR as draft if it is not ready to be reviewed yet.
• I have made sure that the title of my PR follows Commit naming conventions (e.g. feat: adding new MAPDL command)

[Copilot]

Pull Request Overview

This PR removes the version constraint on the PyVista dependency from the project's pyproject.toml file. The change eliminates the upper bound limit that previously restricted PyVista to version 0.45.3 or lower, allowing the project to use newer versions of PyVista without dependency conflicts.

• Removes PyVista version constraint <=0.45.3 from dependencies

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