Support multi-threaded writing of Parquet files with modular encryption

[adamreeve]

See https://github.com/apache/arrow-rs/pull/7111/files#r2015196618

#7111 adds support for writing Parquet files with modular encryption but this only works when using an ArrowWriter to write Arrow record batches. There isn't a way to implement concurrent writing of separate columns using an ArrowColumnWriter with encryption.