Implement percentage functions for random number generation

[Manya7547]

• Added synchronous percentage() function to generate random percentages (0 to 1) with optional repetition.
• Implemented asynchronous percentageAsync() function to generate random percentages asynchronously with optional repetition.
• Created AsyncStream.percentage() to wrap percentageAsync() in an async stream.
• Added Stream.percentage() to wrap percentage() in a synchronous stream.
• Included error handling for negative repetitions using InvalidArgumentError.

These changes introduce support for both synchronous and asynchronous random percentage generation with flexible iteration options.