another caller responsibility for fetch_into_unchecked

Author: rustopian

sdk/pinocchio/src/sysvars/slot_hashes/raw.rs

@@ -109,7 +109,9 @@ pub fn fetch_into(buffer: &mut [u8], offset: usize) -> Result<usize, ProgramErro
 /// The caller is responsible for ensuring that:
 /// 1. `buffer` is large enough for the requested `offset + buffer.len()` range and
 ///    properly laid out (see `validate_buffer_size` and `validate_fetch_offset`).
-/// 2. The memory behind `buffer` is writable for its full length.
+/// 2. `offset + buffer.len()` is not greater than `MAX_SIZE`, or the syscall will
+///    fail.
+/// 3. The memory behind `buffer` is writable for its full length.
 ///
 /// # Safety
 /// Internally this function performs an unchecked Solana syscall that writes