Splink4: database_api contains imports that are not installed by default (e.g. pyspark)

[RobinL]

https://github.com/moj-analytical-services/splink/blob/4271722acd153d792f4ef9b9f68e09c537516959/splink/database_api.py#L14

[ADBond]

Think it would be probably good to break this module up eventually anyhow, maybe something like

database_api/ ├─ init.py # imports DuckDBAPI, SparkAPI etc ├─ database_api.py # core definition ├─ duckdb_api.py # DuckDBAPI ...

but probably want to think a bit about the whole module structure to see what will make the most sense

[RobinL]

Has been fixed in splink4