Include isort

[glatterf42]

Summary

This PR introduces isort as a dependency in the dev group. It also tries to update anyio and pandas to their latest versions allowed by our pyproject.toml.

Context

isort is a tool for sorting and organizing import statements. Code contributions to the MESSAGE stack are checked for compliance, so I think we will want to use it for ixmp4, too, for consistency alone. I also think it does make the imports more readable.
isort offers compatibility with black and should be easily configurable to run automatically whenever saving code files. For vscode, use the official isort extension and edit the settings to read

  "[python]": {
    "editor.defaultFormatter": "ms-python.black-formatter",
    "editor.formatOnSave": true,
    "editor.codeActionsOnSave": {
        "source.organizeImports": true
    },
  },
  "black-formatter.importStrategy": "fromEnvironment",
  "isort.args":["--profile", "black"],
  "isort.importStrategy": "fromEnvironment",

These settings are partly redundant with our pyproject.toml, which also reads

[tool.isort]
profile = "black"

The importStrategy ensures that the tools from the virtual environment are used, if they are present. If not, some default versions will be used. isort.args enables the black compatibility.

[glatterf42]

Importing both sql and sql.ColumnCollection explicitly seems a little redundant.

[meksor]

Obviously I can't check every single file, but it looks alright from what i can see.