Fix dataset paths when --scale-format-string is used

[melissalinkert]

Fixes #179.

This removes trailing slashes (as would be present with --scale-format-string '%2$d/') so that the relative dataset path is not empty.

The associated test should fail without the change to Converter, and pass with it. Independent of the test, something like the command in #179 can be used:

$ bioformats2raw -p input.fake output.zarr --scale-format-string '%2$d/'
$ bioformats2raw -p input.fake output-minimal.zarr --scale-format-string '%2$d/' --no-root-group --no-ome-meta-export

Without this PR, in both cases the *.zarr/.zattrs should have empty path attributes on each of the datasets. With this PR, both commands should result in path being populated with something that exists relative to the .zattrs location.

[sbesson]

The change looks good and adds support for the presence of a trailing slash (which is the default example in the README).

Confirmed the additional asserts introduced in the unit tests fail without the Converter fix when trailing slashes are appended and pass with the fix.

Also tested locally using the two scenarios proposed in the description

(java11) sbesson@Sebastiens-MacBook-Pro-2 bioformats2raw % ./bioformats2raw-0.6.0/bin/bioformats2raw test.fake  --scale-format-string '%2$d/' out_060.zarr
(java11) sbesson@Sebastiens-MacBook-Pro-2 bioformats2raw % ./bioformats2raw-0.6.0/bin/bioformats2raw test.fake --scale-format-string '%2$d/' out_060_minimal.zarr  --no-root-group --no-ome-meta-export
(java11) sbesson@Sebastiens-MacBook-Pro-2 bioformats2raw % ./bioformats2raw-0.7.0-SNAPSHOT/bin/bioformats2raw test.fake  --scale-format-string '%2$d/' out_070_SNAPSHOT.zarr
(java11) sbesson@Sebastiens-MacBook-Pro-2 bioformats2raw % ./bioformats2raw-0.7.0-SNAPSHOT/bin/bioformats2raw test.fake  --scale-format-string '%2$d/' out_070_SNAPSHOT_minimal.zarr  --no-root-group --no-ome-meta-export

A recursive diff indicates the only difference is the value of the path fields in the multiscales metadata which are updated from empty strings to valid paths

(java11) sbesson@Sebastiens-MacBook-Pro-2 bioformats2raw % diff -ur out_060.zarr out_070_SNAPSHOT.zarr 
diff -ur out_060.zarr/.zattrs out_070_SNAPSHOT.zarr/.zattrs
--- out_060.zarr/.zattrs	2022-12-12 09:47:52.000000000 +0000
+++ out_070_SNAPSHOT.zarr/.zattrs	2022-12-12 09:48:22.000000000 +0000
@@ -22,13 +22,13 @@
     } ],
     "name" : "test",
     "datasets" : [ {
-      "path" : "",
+      "path" : "0",
       "coordinateTransformations" : [ {
         "scale" : [ 1.0, 1.0, 1.0, 1.0, 1.0 ],
         "type" : "scale"
       } ]
     }, {
-      "path" : "",
+      "path" : "1",
       "coordinateTransformations" : [ {
         "scale" : [ 1.0, 1.0, 1.0, 2.0, 2.0 ],
         "type" : "scale"
(java11) sbesson@Sebastiens-MacBook-Pro-2 bioformats2raw % diff -ur out_060_minimal.zarr out_070_SNAPSHOT_minimal.zarr 
diff -ur out_060_minimal.zarr/.zattrs out_070_SNAPSHOT_minimal.zarr/.zattrs
--- out_060_minimal.zarr/.zattrs	2022-12-12 09:48:01.000000000 +0000
+++ out_070_SNAPSHOT_minimal.zarr/.zattrs	2022-12-12 09:48:43.000000000 +0000
@@ -22,13 +22,13 @@
     } ],
     "name" : "test",
     "datasets" : [ {
-      "path" : "",
+      "path" : "0",
       "coordinateTransformations" : [ {
         "scale" : [ 1.0, 1.0, 1.0, 1.0, 1.0 ],
         "type" : "scale"
       } ]
     }, {
-      "path" : "",
+      "path" : "1",
       "coordinateTransformations" : [ {
         "scale" : [ 1.0, 1.0, 1.0, 2.0, 2.0 ],
         "type" : "scale"