Add .copy() term entry for Python deque (Issue #7757)

[ylevental]

Description

This PR adds a new term entry for the .copy() method under Python deque. The entry includes:

• A description of the method
• Syntax section with parameters and return value details
• Example section demonstrating assignment vs .copy() behavior
• Codebyte example with interactive code showing reference vs copy
• Shallow copy explanation

The new entry is located at content/python/concepts/deque/terms/copy/copy.md.

Issue Solved

Closes #7757

Type of Change

• Adding a new entry

Checklist

• All writings are my own.
• My entry follows the Codecademy Docs style guide.
• My changes generate no new warnings.
• I have performed a self-review of my own writing and code.
• I have checked my entry and corrected any misspellings.
• I have made corresponding changes to the documentation if needed.
• I have confirmed my changes are not being pushed from my forked main branch.
• I have confirmed that I'm pushing from a new branch named after the changes I'm making.
• I have linked any issues that are relevant to this PR in the Issues Solved section.

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### **Step 3: Verify**

The new PR should show **ONLY** one file changed:

content/python/concepts/deque/terms/copy/copy.md

[mamtawardhani]

Looks good for a second review! 🚀

[Radhika-okhade]

The entry looks good to be merged.

[github-actions]

👋 @ylevental
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