Pinned versions as pyproject requirements

[mpatrou]

Short description of the changes:

pyproject.toml updated with pinned versions for some dependencies. Also channel reordering in the environment file

Check list for the pull request

• [ ] I have read the [CONTRIBUTING]
• [ ] I have read the [CODE_OF_CONDUCT]
• [ ] I have added tests for my changes
• [ ] I have updated the documentation accordingly

Check list for the reviewer

• [ ] I have read the [CONTRIBUTING]
• [ ] I have verified the proposed changes
• [ ] best software practices
  • [ ] all internal functions have an underbar, as is python standard
  • [ ] clearly named variables (better to be verbose in variable names)
  • [ ] code comments explaining the intent of code blocks
• [ ] All the tests are passing
• [ ] The documentation is up to date
• [ ] code comments added when explaining intent

Manual test for the reviewer

References

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 88.79%. Comparing base (79cc9c9) to head (a905990).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## next #155 +/- ## ======================================= Coverage 88.79% 88.79% ======================================= Files 23 23 Lines 1392 1392 ======================================= Hits 1236 1236 Misses 156 156 ```

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