CI: Add Non-Blocking Notebook Spell Check with PR Commenting

[yaugenst-flex]

Spelling errors within Markdown cells or comments in notebooks currently go mostly unnoticed. We want to catch these errors.

The aim of this PR is to inform developers rather than block merging, as there can be false positives in the spell check.

Changes Implemented:

1. spellcheck.py: Executed as part of the notebooks-linting workflow.
2. Targeted Execution: The spell check runs only on .ipynb files that have been modified within the context of the specific pull request. This is achieved using the tj-actions/changed-files action.
3. Non-Blocking Check: The spell check step is configured with continue-on-error: true. This means that even if spellcheck.py finds errors and exits with a non-zero status code, the overall CI workflow will not fail. Linting failures will still cause the workflow to fail as before.
4. PR Commenting: If spellcheck.py detects any spelling errors or encounters issues processing a file, its formatted output is captured and posted as a comment directly on the PR, see here for example.

Closes #207

[tomflexcompute]

This is actually great. I ran the spellchecker only on markdown cells instead of the code cells. I'll fix these typos in the other PR.

[daquinteroflex]

Went thought the action, nice, quite like the logic! Looks good

[daquinteroflex]

Looks good broadly!

[github-actions]

Spell Check Report

AdjointPlugin12LightExtractor.ipynb:

193: "This function includes a circular region of constant permittivity value surrounding the QE. The objective here is to protect the QE from etching. In applications such as single photon sources, a larger unperturbed region surrounding the QE can be helpful to reduce linewidth broadening, as stated in `J. Liu, K. Konthasinghe, M. Davanco, J. Lawall, V. Anant, V. Verma, R. Mirin, S. Nam, S. Woo, D. Jin, B. Ma, Z. Chen, H. Ni, Z. Niu, K. Srinivasan, \"Single Self-Assembled InAs/GaAs Quantum Dots in Photonic Nanostructures: The Role of Nanofabrication,\" Phys. Rev. Appl. 9(6), 064019 (2018)` [DOI: 10.1103/PhysRevApplied.9.064019](https://link.aps.org/doi/10.1103/PhysRevApplied.9.064019)."
	Nam ==> Name

---

Autograd12LightExtractor.ipynb:

178: "This function includes a circular region of constant permittivity value surrounding the QE. The objective here is to protect the QE from etching. In applications such as single photon sources, a larger unperturbed region surrounding the QE can be helpful to reduce linewidth broadening, as stated in `J. Liu, K. Konthasinghe, M. Davanco, J. Lawall, V. Anant, V. Verma, R. Mirin, S. Nam, S. Woo, D. Jin, B. Ma, Z. Chen, H. Ni, Z. Niu, K. Srinivasan, \"Single Self-Assembled InAs/GaAs Quantum Dots in Photonic Nanostructures: The Role of Nanofabrication,\" Phys. Rev. Appl. 9(6), 064019 (2018)` [DOI: 10.1103/PhysRevApplied.9.064019](https://link.aps.org/doi/10.1103/PhysRevApplied.9.064019)."
	Nam ==> Name

---

Checked 47 notebook(s). Found spelling errors in 2 file(s).
Generated by GitHub Action run: https://github.com/flexcompute/tidy3d-notebooks/actions/runs/14490211958

[yaugenst-flex]

I ran the spell check on all notebooks and fixed the remaining typos. So everything should be clean for now. The remaining spell check errors are false positives that we can ignore. They won't pop up again unless the respective notebooks are changed.

[tomflexcompute]

Great addition to the workflow!