Update smart-pointers.md: transfer of ownership

[ArchakGoel]

Added the concept about transfer of ownership limitations between smart and unique pointers.

Description

Added a small subtopic on transfer of ownership limitations for smart pointers.

Issue Solved

Type of Change

• Updating the documentation

Checklist

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

[CLAassistant]

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