Reinstate tomopy

[danielballan]

In the last month or two, our CD build broke because mamba was unable to solve for tomopy. The symptom on GH Actions was just a hang in mamba update ... step (not sure why) but locally I was able to get a clear error message:

$ time micromamba create -f binder/environment.yml  -p from_file --dry-run

                                           __
          __  ______ ___  ____ _____ ___  / /_  ____ _
         / / / / __ `__ \/ __ `/ __ `__ \/ __ \/ __ `/
        / /_/ / / / / / / /_/ / / / / / / /_/ / /_/ /
       / .___/_/ /_/ /_/\__,_/_/ /_/ /_/_.___/\__,_/
      /_/

warning  libmamba 'from_file' does not contain any filesystem separator.
    It will be handled as env name, resulting to the following
    'target_prefix': '/home/dallan/micromamba/envs/from_file'
    If 'target_prefix' is expressed as a relative directory to
    the current working directory, use './some_prefix'
conda-forge/linux-64                                        Using cache
conda-forge/noarch                                          Using cache
nsls2forge/linux-64                                           No change
nsls2forge/noarch                                             No change
Encountered problems while solving:
  - nothing provides __cuda needed by libtomo-1.12.1-cuda10.2h1234567_101

The environment can't be solved, aborting the operation
error    libmamba Could not solve for environment specs
critical libmamba UnsatisfiableError

real	8m21.838s
user	8m19.396s
sys	0m1.742s

In #46 I removed tomopy to resolve the issue.