Added 3Sum and 4Sum algorithms in leetcode

[kbadal19]

Description of Change

Added 3Sum and 4Sum algorithms implementation in C in leetcode section

References

Checklist

• Added description of change
• Added file name matches File name guidelines
• Relevant documentation/comments is changed or added
• PR title follows semantic commit guidelines
• Search previous suggestions before making a new one, as yours may be a duplicate.
• I acknowledge that all my contributions will be made under the project's license.

Notes: These implementations are quite important for people trying to grasp basic concepts within heavy operations in leetcode problems.

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[github-actions]

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