[docs] p-adic: Update docs to change printing-mode=digits to digits-unicode

[gulshan-123]

📝 Checklist

In #41276, I added the printing mode='digits-unicode' in p-adic printing.
This addition was to avoid ... being treated as wildcard in pydoctest module. digits-unicode replaced ... with unicode …

This PR updates the doc to solve the problem.
I updated the docstring as well as the doctest to reflect the new change.

• The title is concise and informative.
• The description explains in detail what this PR is about.
• I have linked a relevant issue or discussion.
• I have created tests covering the changes.
• I have updated the documentation and checked the documentation preview.

⌛ Dependencies

[user202729]

you mean to link to #41276 instead of #41270 .

[gulshan-123]

Do we need to update docs in other files such as padics/factory.py, padics/relaxed_template.pxi, etc..

These are very long files, and will need more time to edit those. The current file will render here: doc-preview, which has a summary of all printing mode...

[github-actions]

Documentation preview for this PR (built with commit 9ac8127; changes) is ready! 🎉
This preview will update shortly after each push to this PR.

[user202729]

If it is useful, there's a sage --fixdoctests tool that automatically fix the output for you. The input probably need manual editing though (or a search-and-replace)

Do we need to update docs in other files such as padics/factory.py, padics/relaxed_template.pxi, etc..

I'd say "strictly speaking not necessary", just that the new doctest is nice to have if someone want to avoid the test being too loose.