feat: implement inner join

src/ir/distribution.rs

src/ir/distribution/tests.rs

src/ir/expression.rs

src/ir/expression/tests.rs

src/ir/operator.rs

src/ir/operator/tests.rs

tests/artifactory/ir/distribution/join_unite_keys.yaml

tests/artifactory/ir/distribution/shrink_dist_key_1.yaml

tests/artifactory/ir/distribution/shrink_dist_key_2.yaml

tests/artifactory/ir/distribution/shuffle_dist_key.yaml

...artifactory/ir/distribution/union_fallback_to_random.yaml

tests/artifactory/ir/distribution/union_preserve_dist.yaml

tests/artifactory/ir/operator/join.yaml