fix(table): AddFiles: close file after usage and parallelize

[starpact]

Previously files are closed only after the whole iteration finishes:

iceberg-go/table/arrow_utils.go

Line 1372 in 55bdfbf

defer rdr.Close()

causing resource leak within a single filesToDataFiles invocation as the file holds an open S3 read stream:

iceberg-go/io/gocloud/blob.go

Line 39 in 55bdfbf

*blob.Reader

A sample trace can demonstrate it clearly:

Besides, I also added parallelism to AddFiles.

Future improvements:
Parallelism partially "fixes" the performance issue of AddFiles but a more fundamental improvement is related to IO, currently for extracting Parquet metadata, the IO layer needs to:

1. do one GetObject and hold the read stream. The size is used by Seek, but the reader is never used(but still consumes quite some memory due to underlying buffering)
2. do one range GetObject for the last 8 bytes
3. do one range GetObject for the footer

A common trick is optimistically prefetching the footer(e.g. 512KB) to coleasce the above 3 requests. However, this requires leaking the IO abstraction, e.g. by determining the file format from the path and returning different implementations accordingly, which may require more discussions.