Function random_walkable_continuous_nearby 

pub fn random_walkable_continuous_nearby<R: Rng>(
    pos: (f64, f64),
    radius: f64,
    walkmap: &[bool],
    grid_w: usize,
    grid_h: usize,
    extent_x: f64,
    extent_y: f64,
    periodic: bool,
    rng: &mut R,
) -> Option<(f64, f64)>

Returns a random walkable continuous position within Euclidean radius r of pos.

Finds walkable grid cells near pos, picks one randomly, then returns a random continuous position within that cell that is within r of pos.

Returns None if no walkable cells exist nearby.