chore: remove dead Rust column-reader code

The JVM-side Parquet column readers were deleted in the previous commit;
the Rust JNI methods and supporting modules they called are now dead.

- parquet/mod.rs: drop JNI methods initColumnReader, setDictionaryPage,
  setPageV1, setPageV2, resetBatch, readBatch, skipBatch, currentBatch,
  closeColumnReader, plus the Context/get_reader helpers.
- Delete parquet/read/ (column, levels, values, mod), mutable_vector.rs,
  data_type.rs, and the util sub-modules bit_packing, buffer, memory,
  test_common that only existed for the column readers.
- Trim parquet/util/jni.rs to deserialize_schema (the only helper used
  by the surviving Arrow-native scan path).
- Delete native/core/src/common/ entirely; bit.rs and buffer.rs were
  only consumed by the deleted parquet column-reader chain.
- Drop the parquet_read, bit_util, and parquet_decode benches that
  exercised the removed code; deregister them from Cargo.toml.

Author: andygrove

native/core/Cargo.toml

@@ -109,18 +109,6 @@ name = "comet"
 # "rlib" is for benchmarking with criterion.
 crate-type = ["cdylib", "rlib"]
 
-[[bench]]
-name = "parquet_read"
-harness = false
-
-[[bench]]
-name = "bit_util"
-harness = false
-
-[[bench]]
-name = "parquet_decode"
-harness = false
-
 [[bench]]
 name = "array_element_append"
 harness = false