* Improve database type inference
Python's DBAPI isn't super clear and homogeneous on the
cursor.description specification, and this PR attempts to improve
inferring the datatypes returned in the cursor.
This work started around Presto's TIMESTAMP type being mishandled as
string as the database driver (pyhive) returns it as a string. The work
here fixes this bug and does a better job at inferring MySQL and Presto types.
It also creates a new method in db_engine_specs allowing for other
databases engines to implement and become more precise on type-inference
as needed.
* Fixing tests
* Adressing comments
* Using infer_objects
* Removing faulty line
* Addressing PrestoSpec redundant method comment
* Fix rebase issue
* Fix tests
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