Dynamic units in buffer dialog

[mfisher87]

Description

This PR includes all changes from #544; rebase after merge. I did this because to show this PR in this repo, I needed to target a branch in this repo, not a branch on Arjun's fork.

Resolves #541

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• PR description contains references to any issues the PR resolves, e.g. Resolves #XXX.
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📚 Documentation preview: https://jupytergis--554.org.readthedocs.build/en/554/
💡 JupyterLite preview: https://jupytergis--554.org.readthedocs.build/en/554/lite

[github-actions]

👈 Launch a Binder on branch mfisher87/jupytergis/dynamic-units

[martinRenou]

@mfisher87 @arjxn-py @kpdavi what would you think of splitting this PR in two?

• one PR that removes the projection parameter for the buffer processing function (as we discussed during the hackathon, we should probably stay close to the QGIS behavior and not allow to re-project whilst buffering)
• one PR that investigates having a dynamic unit description. This may be a bit more involved as we thought, as we're missing the projection information of the currently selected layer.

First PR is easy to fix, second less easy, hence I'd like to suggest splitting the PR

[mfisher87]

Great call. Let's leave this PR as a draft and create a new PR for removing reprojection support from the buffer op.

[arjxn-py]

Sounds Good to me too

[mfisher87]

#563