Implements std.PaddedArray as a companion to std.BoundedArray

[ikskuh]

This is a bare bones implementation of a padded array. These are similar to a sentinelled array, but the sentinel is only used for implicit length determination.

These kind of arrays are often used in C APIs inside of structs to store strings up to a length of N. Thus, a padded array alias was exported from std.c.CharArray, so people can easily interact with C APIs that use this kind of strings.

If wanted, i can add the usual container APIs that are also present in std.BoundedArray, as long as they are useful. Stuff like .resize() doesn't make much sense on this kind of type, but functions like .append() or a .writer() could definitly be useful.