Removed recursion from lfs_dir_traverse
Removed recursion from lfs_dir_traverse

lfs_dir_traverse is a bit unpleasant in that it is inherently a
recursive function, but without a strict bound of 4 calls (commit -> filter ->
move -> filter), and efforts to unroll the recursion comes at a
signification code cost.

It turns out the best solution I've found so far is to simple create an
explicit stack with an explicit bound of 4 calls (or more accurately,
3 pushed frames).

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This actually highlights one of the bigger flaws in littlefs right now,
which is that this function, lfs_dir_traverse, takes O(n^2) disk reads
to traverse.

Note that LFS_FROM_MOVE can only occur once per commit, which is why
this code is O(n^2) and not O(n^4).

littlefs-project/littlefs,littlefs-project/littlefs