pandas: STYLE Increase coverage of inconsistent-namespace-usage

If you already have experience contributing, then please leave this issue to newcomers - thanks 👍

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In .pre-commit-config.yaml, the check inconsistent-namespace-usage is limited to pandas/tests/frame/. Let’s expand it to the rest of pandas/tests/.

The task here is:

1. make sure you’re familiar with the contributing guide
2. choose a folder from the list below (e.g. series) and add it to the check in .pre-commit-config.yaml. E.g., if you chose series, that would be:

    -   id: inconsistent-namespace-usage
        name: 'Check for inconsistent use of pandas namespace in tests'
        entry: python scripts/check_for_inconsistent_pandas_namespace.py
        language: python
        types: [python]
        files: ^pandas/tests/(frame|series)/

1. temporarily add tokenize-rt as an additional dependency and --replace as an arg (these will be removed later):

    -   id: inconsistent-namespace-usage
        name: 'Check for inconsistent use of pandas namespace in tests'
        entry: python scripts/check_for_inconsistent_pandas_namespace.py
        language: python
        types: [python]
        files: ^pandas/tests/(frame|series)/
        additional_dependencies: [tokenize-rt]
        args: [--replace]

1. run this check on all files with pre-commit, i.e.:

  $ pre-commit run inconsistent-namespace-usage --all-files
  [INFO] Initializing environment for local:tokenize-rt.
  [INFO] Installing environment for local.
  [INFO] Once installed this environment will be reused.
  [INFO] This may take a few minutes...
  Check for inconsistent use of pandas namespace in tests.......................Failed
  - hook id: inconsistent-namespace-usage
  - files were modified by this hook

1. run it again - this time, it should pass

$ pre-commit run inconsistent-namespace-usage --all-files
Check for inconsistent use of pandas namespace in tests.......................Passed

Check that the other hooks still pass - if you enable pre-commit (pre-commit install), then this will happen automatically when you try to commit your changes (see step 6)

1. revert the changes to .pre-commit-config.yaml (we’ll update it once these changes are all so as to avoid a barrage of merge conflicts)
2. commit your changes, and open a pull request. Check over your changes, make sure they look sensible, let me know if not

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Here are the folders in pandas/tests which this check needs expanding to:

• series
• scalar
• resample
• util
• tseries
• dtypes
• arrays
• plotting
• tools
• indexing
• strings
• reductions
• frame
• arithmetic
• config
• api
• generic
• io
• base
• window
• internals
• reshape
• computation
• apply
• groupby
• tslibs
• libs
• indexes
• extension

No need to ask for permission to work on this, just leave a comment letting people know which folder(s) from the list above you’re working on