Function encode_varint 

pub fn encode_varint(value: u64, buf: &mut [u8; 10]) -> usize

Encode an unsigned 64-bit integer as LEB128 into buf. Returns the number of bytes written (1–10).

use crous_core::varint::encode_varint;
let mut buf = [0u8; 10];
assert_eq!(encode_varint(0, &mut buf), 1);
assert_eq!(buf[0], 0x00);

assert_eq!(encode_varint(127, &mut buf), 1);
assert_eq!(buf[0], 0x7f);

assert_eq!(encode_varint(128, &mut buf), 2);
assert_eq!(&buf[..2], &[0x80, 0x01]);

assert_eq!(encode_varint(300, &mut buf), 2);
assert_eq!(&buf[..2], &[0xac, 0x02]);