Update the write_varint method to use an encoded buffer of size 9 instead of 10.

The SQLite varint specification states that the varint is guaranteed to be a maximum of 9 bytes, but our version of write_varint initializes a buffer of 10 bytes. Changing the size to match the specification.

tests/integration/query_processing/test_btree.rs

@@ -130,7 +130,7 @@ pub fn write_varint(buf: &mut [u8], value: u64) -> usize {
         return 9;
     }
 
-    let mut encoded: [u8; 10] = [0; 10];
+    let mut encoded: [u8; 9] = [0; 9];
     let mut bytes = value;
     let mut n = 0;
     while bytes != 0 {