Added Binary to Gray code

[Craniace]

Description of Change

Added a new algorithm to convert a binary number to its Gray code equivalent in the bit_manipulation directory.
The algorithm performs bitwise XOR between the binary number and its right-shifted version to generate the Gray code.

References

• Wikipedia – Gray code

Checklist

• Added description of change
• Added file name matches File name guidelines
• Added tests and example, test must pass
• Relevant documentation/comments is changed or added
• PR title follows semantic commit guidelines
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• I acknowledge that all my contributions will be made under the project's license.

Notes:
Added binary_to_gray.c — a simple and efficient implementation using bitwise operators with example and validation logic.