Feature: Add MINO implementation.

[samuelburbulla]

Feature: Add MINO implementation.

Description

Add the mesh-independent neural operator (MINO).

Reference: Seungjun Lee. Mesh-Independent Operator Learning for Partial Differential Equations. 2nd AI4Science Workshop, ICML (2022)

Which issue does this PR tackle?

• Adds MINO.

How does it solve the problem?

• Implements AttentionKernel and MINO class.

How are the changes tested?

• Added test_mino.

Checklist for Contributors

• [ ] Scope: This PR tackles exactly one problem.
• [ ] Conventions: The branch follows the feature/title-slug convention.
• [ ] Conventions: The PR title follows the Bugfix: Title convention.
• [ ] Coding style: The code passes all pre-commit hooks.
• [ ] Documentation: All changes are well-documented.
• [ ] Tests: New features are tested and all tests pass successfully.
• [ ] Changelog: Updated CHANGELOG.md for new features or breaking changes.
• [ ] Review: A suitable reviewer has been assigned.

Checklist for Reviewers:

• [ ] The PR solves the issue it claims to solve and only this one.
• [ ] Changes are tested sufficiently and all tests pass.
• [ ] Documentation is complete and well-written.
• [ ] Changelog has been updated, if necessary.