update rayon iterator for fast failures

[gregl83]

Rayon is used to parallelize iterating over source paths and hashing file contents; however, if an operating system failure (e.g., locked file) occurs the iterator doesn't immediately fail.

A feature introduced the panic_fuse() function on rayon iterators that terminates iterator threads when a panic occurs leading to a fast failure and ultimately a failed attempt at producing a paq hash but without delay.

There is potentially a near negligible performance degradation that MUST be tested thoroughly if this feature is implemented.