Bugfix: allow for more complex specs to be checked properly

[lauramaxwell]

Expected Behavior

users should be able to require _all columns of a given df, and also specify type for specific columns in specs and checkSpec() will check those columns appropriately, See below for example spec.

Current Behavior

right now checkSpec() doesn't check those columns because _all is used for required, so it currently skips the type step as well due to some faulty logic.

Possible Solution

updated logic in checkSpec to

Steps to Reproduce

Context (Environment)

Possible Implementation

Additional Comments