Fix file watch for paths containing percent-encoded characters

[stephanedupont]

Fixes #15

setUpFileWatch() builds the path it passes to open(_:O_EVTONLY) from directoryURL.path(). URL.path() defaults to percentEncoded: true, so any directory whose path contains characters that get percent-encoded (most commonly a space) is handed to open() still encoded.

For example, the default Application Support location becomes:

.../Library/Application%20Support/<bundleID>/...

open() expects a real filesystem path, not a URL-encoded one. There is no directory literally named Application%20Support, so open() returns -1, the fileDescriptor > 0 guard fails, and the watch silently fails with:

Failed to set up file watch due to invalid file descriptor

This affects any store placed under Library/Application Support (Apple's recommended location for this kind of file). Reads/writes are unaffected because they go through NSFileCoordinator/URL-based APIs; only the open()-based watch breaks.

Using path(percentEncoded: false) passes a properly decoded filesystem path to open(), so the watch sets up correctly.