Read a directory's own json before those of its subdirectories

[TheLastDarkthorne]

findFiles() returns each json in filesystem order, createItems() adds
items in that same order, and mergeDown() keeps the position of whichever
occurrence it merges first. So a group only holds the position declared in
its parent's json if that json happens to be read before its subdirectories'
jsons. eachFileRecurse frequently reads a subdirectory's json first, and
the group is then positioned by directory-visit order instead of by its
declared position - subgroups get hoisted ahead of leaf items and end up
sorted by name.

This matters because Mudlet evaluates triggers in tree order, so a reordered
group can change which trigger sees a line first. Converting an existing
~2,500-trigger package with this bug present, 19 of 381 groups came out
reordered, including one whose first child was an anti-illusion group that
ended up in the middle of the list instead.

Fixes #44. Likely also the cause of #14, where folders come out sorted by
neither name nor creation date - directory-visit order looks exactly that
arbitrary from outside.

The fix

Sort findFiles()'s result shallowest-first, breaking ties by path.

The tie-break matters as much as the depth does. eachFileRecurse returns
directory entries in whatever order the platform's filesystem gives -
alphabetical on NTFS, effectively arbitrary on ext4 - and a group that no
parent json declares takes its position from read order regardless. Without
a total order, the same sources build a differently ordered package on a
different machine. That is how the depth-only version of this fix was caught
as still-incomplete: a package that verified clean on Windows came out
reordered when the identical commit was built on a Linux CI runner. Breaking
ties by path removes the platform dependence entirely.

Verification

Caught and verified converting an existing ~2,500-trigger, 120-alias, 25-module
Mudlet package to a muddler project: comparing the built package against the
25 hand-authored originals object-by-object (structure, names, load order)
found 19 reordered groups before this fix and none after, on both a Windows
build and a from-scratch Linux CI build of the same commit.

Runnable reproduction

https://github.com/TheLastDarkthorne/mudlet-tooling-repros/tree/main/muddler/bug7-directory-read-order

Run against the stock 1.1.0 jar, Outer's children come out as Alpha then
Beta - alphabetical directory-scan order - instead of the declared Beta
then Alpha. run_repros.py in the same directory builds it against both a
stock and a patched jar and prints the resulting tree for both.