Added math and bit manipulation snippets for java

[Mcbencrafter]

Description

Added snippets for java including:

1. Math

• calculating the greatest common divisor (gcd) and the least common multiple (lcm) of two numbers
• calculating a checksum of a number
• calculating the factorial of a number
• calculating the nth fibonacci number
• checking if a number is a prime

2. Bit Manipulation

• checking if number is a power of two
• counting the bits in an int

I also capataliezed the titles of date/time snippets because they did look weird and most snippet titles are already capataliezed.

Type of Change

• ✨ New snippet
• 🛠 Improvement to an existing snippet
• 🐞 Bug fix
• 📖 Documentation update
• 🔧 Other (please describe):

Checklist

• I have tested my code and verified it works as expected.
• My code follows the style and contribution guidelines of this project.
• Comments are added where necessary for clarity.
• Documentation has been updated (if applicable).
• There are no new warnings or errors from my changes.

Related Issues

None

Additional Context

Screenshots (Optional)

Click to view screenshots

[Mathys-Gasnier]

A little change, but overall great work

[Mcbencrafter]

I noticed I forgot to copy an import to the snippet, should be fine now