feat: add CI and Codecov badges to README and set up Codecov integration (#16)

* feat: add CI and Codecov badges to README

* fix: correct workflow filename in CI badges

* fix: update Codecov badge to include authentication token

* fix: use ci.yml for CI badge to resolve Check Links failure

* revert: remove build.yml workflow changes per review feedback

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Co-authored-by: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>

Author: jamesbhobbs

README.md

@@ -1,5 +1,8 @@
 # jupyterlab_deepnote
 
+[![CI](https://github.com/deepnote/jupyterlab-deepnote/actions/workflows/ci.yml/badge.svg?branch=main)](https://github.com/deepnote/jupyterlab-deepnote/actions/workflows/ci.yml)
+[![codecov](https://codecov.io/gh/deepnote/jupyterlab-deepnote/graph/badge.svg?token=OV32VZNOJ2)](https://codecov.io/gh/deepnote/jupyterlab-deepnote)
+
 A Deepnote extension for JupyterLab
 
 This extension is composed of a Python package named `jupyterlab_deepnote`