Add note on possible exceptions to extensions docs

[duckontheweb]

Related Issue(s):

• Docs on adding extensions is misleading or incomplete #602

Description:

Adds a note to the Concepts docs describing how to access extension properties that makes it more clear that .ext will raise an exception if the object does not already implement the extension.

PR Checklist:

• Code is formatted (run pre-commit run --all-files)
• Tests pass (run scripts/test)
• Documentation has been updated to reflect changes, if applicable
• This PR maintains or improves overall codebase code coverage.
• Changes are added to the CHANGELOG. See the docs for information about adding to the changelog.

[codecov-commenter]

Codecov Report

Merging #701 (f2408e8) into main (ddafad4) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #701   +/-   ##
=======================================
  Coverage   94.30%   94.30%           
=======================================
  Files          77       77           
  Lines       11249    11249           
  Branches     1342     1342           
=======================================
  Hits        10608    10608           
  Misses        461      461           
  Partials      180      180           

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update ddafad4...f2408e8. Read the comment docs.

[alexgleith]

I think that looks good! Thanks :-)