Fixed excessive waste from overly large inline files

Before this, there were some safety limits, but there was no real
default limit to the size of inline files other than the amount of RAM
available. On PCs, this meant that inline files were free to fill up
directory blocks to a little under the block size.

However this is very wasteful in terms of storage space. Because of
splitting limits to keep the compact runtime reasonable, each byte of an
inline files uses 4x the amount.

Fortunately we can find an optimal inline limit:

Inline file waste for n bytes = 3n
CTZ file waste for n bytes    = B - n

Where B = block size

Solving for n = B/4

So the optimal inline limit is B/4. However, this assumes a perfect inline
file and no metadata. We can decrease this to B/8 to give a bit more
breathing room for directory+file metadata.

lfs.c

@@ -2710,7 +2710,8 @@ lfs_ssize_t lfs_file_write(lfs_t *lfs, lfs_file_t *file,
 
     if ((file->flags & LFS_F_INLINE) &&
             lfs_max(file->pos+nsize, file->ctz.size) >
-            lfs_min(lfs->cfg->cache_size, LFS_ATTR_MAX)) {
+            lfs_min(LFS_ATTR_MAX, lfs_min(
+                lfs->cfg->cache_size, lfs->cfg->block_size/8))) {
         // inline file doesn't fit anymore
         file->off = file->pos;
         int err = lfs_file_relocate(lfs, file);