ENH: Infer dtype from non-nulls when pushing to SQL

Minor cleanup

Minor rename

Simplifying

Code review fixes

Complex numbers

Release note

Release note
Merge pull request #8973 from artemyk/notnulldtype_sql

ENH: Infer dtype from non-nulls when pushing to SQL
DOC: expand docs on sql type conversion
Merge pull request #9038 from jorisvandenbossche/sql-doc-dtype

DOC: expand docs on sql type conversion
Fix timedelta json on windows
Merge pull request #9044 from cpcloud/timedelta-json

Fix timedelta json on windows
unstack with nan in the index