TYP: enable reportMissingImports
reportMissingImports checks whether all libraries can be imported. This requires all dependencies to be installed on the CI that runs pyright.

This flag should probably NOT be enabled, as it would force all contributors to install all dependencies. I'm enabling it temporarily to see whether the CI has all dependencies installed.

edit:
The typing CI has not all packages installed:

```
/home/runner/work/pandas/pandas/pandas/io/clipboard/__init__.py
  /home/runner/work/pandas/pandas/pandas/io/clipboard/__init__.py:150:14 - error: Import "qtpy.QtWidgets" could not be resolved (reportMissingImports)
  /home/runner/work/pandas/pandas/pandas/io/clipboard/__init__.py:155:18 - error: Import "PyQt4.QtGui" could not be resolved (reportMissingImports)
  /home/runner/work/pandas/pandas/pandas/io/clipboard/__init__.py:537:20 - error: Import "AppKit" could not be resolved (reportMissingImports)
  /home/runner/work/pandas/pandas/pandas/io/clipboard/__init__.py:538:20 - error: Import "Foundation" could not be resolved (reportMissingImports)
  /home/runner/work/pandas/pandas/pandas/io/clipboard/__init__.py:557:20 - error: Import "qtpy" could not be resolved (reportMissingImports)
  /home/runner/work/pandas/pandas/pandas/io/clipboard/__init__.py:564:28 - error: Import "PyQt4" could not be resolved (reportMissingImports)
/home/runner/work/pandas/pandas/pandas/io/excel/_pyxlsb.py
  /home/runner/work/pandas/pandas/pandas/io/excel/_pyxlsb.py:36:14 - error: Import "pyxlsb" could not be resolved (reportMissingImports)
  /home/runner/work/pandas/pandas/pandas/io/excel/_pyxlsb.py:41:14 - error: Import "pyxlsb" could not be resolved (reportMissingImports)
```
Install `pyxlsb` but don't bother installing all the platform-dependent code for the clipboard.

Should `PyQt4` be removed? I don't find it on pip and "[PyQt4 and Qt v4 are no longer supported and no new releases will be made.](https://www.riverbankcomputing.com/software/pyqt/)"
 One option could be to enable reportMissingImports but add the following pyright comment to `pandas/io/clipboard/__init__.py`

`# pyright: reportMissingImports=false`

xref https://github.com/pandas-dev/pandas/pull/43751#issuecomment-927323643 looks fine to me. cc @simonjayhawkins  Should probably wait until #43799 to not force contributors to install all dependencies. if you'd rebase (but lgtm). > One option could be to enable reportMissingImports but add the following pyright comment to `pandas/io/clipboard/__init__.py`
> 
> `# pyright: reportMissingImports=false`
> 
> xref [#43751 (comment)](https://github.com/pandas-dev/pandas/pull/43751#issuecomment-927323643)

since clipboard is vendored, happy to exclude from all pyright checks and limit the use of module level comment syntax for pyright to pandas code > Install `pyxlsb` but don't bother installing all the platform-dependent code for the clipboard.

in the pip secction of environment.yml we have some typing stubs imports

```
    - types-python-dateutil
    - types-PyMySQL
    - types-pytz
    - types-setuptools
 ```

if the package has stubs we should include it here.

if it is a typed library like numpy, then we already have it in environment.yaml so the missing import only becomes an issue if an older version of numpy is installed.

I'm not sure what is best for untyped optional libraries without stubs packages.

conda solver is already slow for our pandas-dev environment, but otoh happy to add pyxlsb as our dev env should probably have all optional dependencies installed to ensure local testing catches issues. (having some optional dependencies included in `environment.yml` but not all seems strange)

I assume that as pyxlsb is not a pytyped library and has no stubs, that the imports will resolve to Any. So we gain nothing from a typing perspective other than silencing the pyright warning by adding pyxlsb to `environment.yml`.

So am also happy not to add. > conda solver is already slow for our pandas-dev environment

Fortunately, pyxlsb does not seem to list any dependencies, so it should be quick to resolve :) But enabling the pyright option would also mean that future potentially difficult to resolve packages will be added.

> I assume that as pyxlsb is not a pytyped library and has no stubs, that the imports will resolve to Any. 

Unfortunately, pyxlsb has no type annotations.

> So we gain nothing from a typing perspective other than silencing the pyright warning by adding pyxlsb to `environment.yml`.

We can catch some typos in pyi files. I was just trying flake8-pyi, it wouldn't have caught these two typos.


Let me know what you think is more important. Happy to remove pyxlsb and not disable MissingImports. I'm not against enabling the pyright option so that the typos are caught.

We can enable MissingImports without adding to environment.yaml using the module level pyright options syntax to disable MissingImports in just `pandas/io/excel/_pyxlsb.py` if any objections.

otherwise lgtm.  thanks @twoertwein happy being strict here.