Why

step 2 of #240: replace rusoto_s3 (in use_memory_table: true path) with S3 client from object_store (s3://)

rusoto_s3 is used in columnq::io::s3 and columnq::io::s3 is used in two places:

• columnq::partitions_from_table_source
• columnq::table::delta

we would like to remove rusoto_s3 and switch to object_store, so can unify S3/GCS/Azure in future

How

this PR (part 1) creates columnq::io::object_store and migrate columnq::partitions_from_table_source.
next PR (part 2) will focus on migrating columnq::table::delta and delete columnq::io::s3 completely

Test

Integration tests are improved to include single file and directory.