Minor: consolidate path_partition test into core_integration

[alamb]

Which issue does this PR close?

N/A

Rationale for this change

Each individual .rs file in the tests directory results in a new test binary which means:

• 10s of MB of new binary (and thus slower)
• It can't run in parallel with other tests (only tests within the same binary do)

What changes are included in this PR?

Consolidate the path_partition test into the core_integration test to make testing more efficient

Are these changes tested?

By CI. I also tested locally

You can see the tests run like this:

$ cargo test --test core_integration -- path_partition
   Compiling datafusion-physical-optimizer v40.0.0 (/Users/andrewlamb/Software/datafusion/datafusion/physical-optimizer)
   Compiling datafusion v40.0.0 (/Users/andrewlamb/Software/datafusion/datafusion/core)
    Finished `test` profile [unoptimized + debuginfo] target(s) in 3.92s
     Running tests/core_integration.rs (target/debug/deps/core_integration-c1d878777c00ea56)

running 9 tests
test sql::path_partition::parquet_overlapping_columns ... ok
test sql::path_partition::parquet_statistics ... ok
test sql::path_partition::parquet_multiple_partitions ... ok
test sql::path_partition::parquet_multiple_nonstring_partitions ... ok
test sql::path_partition::csv_projection_on_partition ... ok
test sql::path_partition::csv_filter_with_file_nonstring_col ... ok
test sql::path_partition::csv_filter_with_file_col ... ok
test sql::path_partition::csv_grouping_by_partition ... ok
test sql::path_partition::parquet_distinct_partition_col ... ok

test result: ok. 9 passed; 0 failed; 0 ignored; 0 measured; 200 filtered out; finished in 0.07s

Are there any user-facing changes?

[lewiszlw]

LGTM.

[alamb]

Thanks @lewiszlw