[BUG] Template generation macro doesn't work for derivatives

[oesteban]

Trying to use the template macro with derivatives fails with:

WARNING -  [macros] - ERROR # _Macro Rendering Error_

           _File_: `derivatives/imaging.md`

           _AttributeError_: 'Namespace' object has no attribute 'datatypes'

           ```
           Traceback (most recent call last):
             File "/data/home/oesteban/workspace/bids-specification/tools/schemacode/src/bidsschematools/types/namespace.py", line 220, in
           __getattribute__
               return self[key]
                      ~~~~^^^^^
             File "/data/home/oesteban/workspace/bids-specification/tools/schemacode/src/bidsschematools/types/namespace.py", line 236, in
           __getitem__
               val = mapping[subkey]
                     ~~~~~~~^^^^^^^^
           KeyError: 'datatypes'

           During handling of the above exception, another exception occurred:

           Traceback (most recent call last):
             File "/home/oesteban/.miniconda/envs/bids-spec/lib/python3.11/site-packages/mkdocs_macros/plugin.py", line 688, in render
               return md_template.render(**page_variables)
                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
             File "/home/oesteban/.miniconda/envs/bids-spec/lib/python3.11/site-packages/jinja2/environment.py", line 1301, in render
               self.environment.handle_exception()
             File "/home/oesteban/.miniconda/envs/bids-spec/lib/python3.11/site-packages/jinja2/environment.py", line 936, in handle_exception
               raise rewrite_traceback_stack(source=source)
             File "<template>", line 8, in top-level template code
             File "/data/home/oesteban/workspace/bids-specification/tools/mkdocs_macros_bids/macros.py", line 94, in make_filename_template
               codeblock = render.make_filename_template(
                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
             File "/data/home/oesteban/workspace/bids-specification/tools/schemacode/src/bidsschematools/render/text.py", line 323, in
           make_filename_template
               for datatype in rule.datatypes:
                               ^^^^^^^^^^^^^^
             File "/data/home/oesteban/workspace/bids-specification/tools/schemacode/src/bidsschematools/types/namespace.py", line 222, in
           __getattribute__
               raise err
             File "/data/home/oesteban/workspace/bids-specification/tools/schemacode/src/bidsschematools/types/namespace.py", line 214, in
           __getattribute__
               return super().__getattribute__(key)
                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
           AttributeError: 'Namespace' object has no attribute 'datatypes'

           ```

Originally posted by @oesteban in https://github.com/bids-standard/bids-specification/issues/1781#issuecomment-2686101512

[oesteban]

This problem blocks a list of templates compiled by @effigies from being updated:

https://github.com/bids-standard/bids-specification/blob/0142056a79a292292697cf2bf086618ce12a9a51/src/derivatives/imaging.md?plain=1#L10-L15

https://github.com/bids-standard/bids-specification/blob/0142056a79a292292697cf2bf086618ce12a9a51/src/derivatives/imaging.md?plain=1#L147-L152

https://github.com/bids-standard/bids-specification/blob/0142056a79a292292697cf2bf086618ce12a9a51/src/derivatives/imaging.md?plain=1#L264-L269

https://github.com/bids-standard/bids-specification/blob/0142056a79a292292697cf2bf086618ce12a9a51/src/derivatives/imaging.md?plain=1#L328-L333

https://github.com/bids-standard/bids-specification/blob/0142056a79a292292697cf2bf086618ce12a9a51/src/derivatives/imaging.md?plain=1#L402-L407

https://github.com/bids-standard/bids-specification/blob/0142056a79a292292697cf2bf086618ce12a9a51/src/derivatives/common-data-types.md?plain=1#L180-L185