Improve get and get_mut method signature, Add From implementations for Vec<Vec<T>> and (Vec<T>, usize)

[pcbowers]

While using this library, I found it difficult to get neighbors because of the possibility of overflows when going negative. For instance, to get the neighbor that is up and to the left of the current cell, I would have to something like this:

let row: usize = 0;
let col: usize = 0;
if let Some(row) = row.checked_sub(1) {
    if let Some(col) = col.checked_sub(1) {
        if let Some(cell) = grid.get(row, col) {
            dbg!(cell);
        }
    }
}

This was a lot of code. Ideally, I could just do this:

let row: isize = 0;
let col: isize = 0;
if let Some(cell) = grid.get(row - 1, col - 1) {
    dbg!(cell);
}

Unfortunately, .get and .get_mut do not accept anything but usize, so this would cause an overflow warning.

I started adding this to my rust projects:

trait GetChecked<T> {
    fn get_checked(&self, row: isize, col: isize) -> Option<&T>;
    fn get_checked_mut(&mut self, row: isize, col: isize) -> Option<&mut T>;
}

impl<T> GetChecked<T> for Grid<T> {
    fn get_checked(&self, row: isize, col: isize) -> Option<&T> {
        self.get(row.try_into().ok()?, col.try_into().ok()?)
    }

    fn get_checked_mut(&mut self, row: isize, col: isize) -> Option<&mut T> {
        self.get_mut(row.try_into().ok()?, col.try_into().ok()?)
    }
}

This trait and implementation allowed me to add new methods called get_checked and get_checked_mut to do what I wanted: pass in an isize or any other thing that could be converted into a number. If it was less than 0, it would return None, which is perfect: there wouldn't be a value there anyway!

let row: isize = 1;
let col: isize = 1;
if let Some(cell) = grid.get_checked(row - 1, col - 1) {
    dbg!(cell);
}

After implementing this a couple times, I figured that it was useful enough to contribute to this library, hence this PR. (I also cleaned up some of the clippy linter warnings I was getting! And added implentation for From which makes more sense than adding a from_vec method, making it possible to potentially remove that function one day)

[becheran]

Looks good to me and very useful. Had some mergers before this one which now causes merge conflicts. Could you please rebase to main? Then I will merge this as well.

[Einliterflasche]

I don't know whether this is intentional but I want to note that having a single generic type for both arguments (e.g. fo foo<U: impl Into<usize>(col: U, row: U)) prevents calling the function with two different types even if both implement Into<usize>. This could be allowed if we were to use seperate generic types, like this: fn get_checked(col: impl Into<usize>, row: impl Into<usize>)

[pcbowers]

I don't know whether this is intentional but I want to note that having a single generic type for both arguments (e.g. fo foo<U: impl Into<usize>(col: U, row: U)) prevents calling the function with two different types even if both implement Into<usize>. This could be allowed if we were to use seperate generic types, like this: fn get_checked(col: impl Into<usize>, row: impl Into<usize>)

Good call! That was not intentional. I'll implement your suggestion when I rebase!

[pcbowers]

Looks good to me and very useful. Had some mergers before this one which now causes merge conflicts. Could you please rebase to main? Then I will merge this as well.

@becheran, Should be ready to go! I realized I implemented a merge commit instead of a rebase (force of habit, sorry!). I can undo those commits if you feel strongly about rebasing.