Possible unsound public API

[charlesxsh]

The parameter i lacks of sufficient checks and used directly in get_unchecked under safe public function, which might cause memory risks.

trk-io/src/array_sequence.rs

Lines 162 to 166 in 6f78936

	pub fn length_of_array(&self, i: usize) -> usize {
	let current = unsafe { *self.offsets.get_unchecked(i) };
	let next = unsafe { *self.offsets.get_unchecked(i + 1) };
	next - current
	}

In Rust, we shoud not face memory issues if merely use safe function API.

Suggestion:

1. add sufficient check
2. add unsafe to the function declaration to notify the developer

[nilgoyette]

You're right Thanks for reporting. I do have a simpler suggestion though

pub fn length_of_array(&self, i: usize) -> usize {
    self.offsets[i + 1] - self.offsets[i]
}

because the unsafe was totally useless. If i is wrong, there will be a panic, exactly like Vec does.