Return files ordered by creation time when using `discover`

[felipet]

While trying to find a solution for GH-1, I have found that discover shall return found files using some sort of ordering. Usually, files are listed using their names. As I collect data using the same name stem and adding an index to it, I was not paying too much attention to the order in which discover was returning the files. However, I've found that's a critical aspect while trying to find a solution for GH-1.

According to the documentation of read_dir, no ordering is guaranteed. I guess there would be some cases in which order might not match what is usually expected. This might never happen while working with my data files, but I wanted to avoid future issues due to this. So, I need to enhance the current implementation of discover to ensure some sort of ordering.

[felipet]

Proposal of implementation summited. The new feature relies on the creation time returned by the OS system call (backend of the Rust function read_dir). If data files are manipulated manually to insert data, this function will produce an incorrect ordering. However, I think this implementation is good enough as doing something bulletproof would require a lot of code, and it would address a corner case (data is usually auto-collected sequentially, so manual editions would be controlled).