Create 0707-design-linked-list.rs

[samyaktx]

• File(s) Created: 0707-design-linked-list.rs
• Language(s) Used: rust
• Submission URL: https://leetcode.com/problems/design-linked-list/
  //: # "Getting the Submission URL"
  //: # "Go to the leetcode Submissions tab"
  //: # "and click on the Accepted status of your submission.]"
  //: # "Finally copy the URL from the nav bar, it should look like https://leetcode.com/problems/design-linked-list/"

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