fix(iceberg): Incorrect $partition Metadata in Trino for Iceberg Tables Written via IcebergIO.writeRows with Timestamp Partitioning

[mskyrim]

this fixes the issue raised here #35417
What happened?

We are using an Apache Beam pipeline (v2.62.0) to ingest data read in Protobuf format, transform it into a Beam schema (dynamically), and then write it to an Iceberg table using IcebergIO.writeRows as the final step of the pipeline.
We have noticed an issue when writing to Iceberg tables that are partitioned by the meta_processing_time field using the following specification:
(PartitionSpec.builderFor(contractIcebergSchema).month("meta_processing_time").build())
Although the Parquet data files are correctly written under the expected monthly partition folders (e.g., path/2025-06/filename.parquet), when querying the table using Trino:
select "$partition" , "$path",* from iceberg_table"

The $partition metadata field incorrectly shows a value of "1970-07", while:

the $path value is correctly referencing the meta_processing_time month (e.g., 'path/2025-06/filename.parquet')
the actual meta_processing_time column in the data contains the correct timestamp value (e.g., '2025-06-24 11:06:06.187 +00:00')
After running the following query in Trino:

ALTER TABLE table_name EXECUTE optimize

the $partition value is corrected and shows the expected value '2025-06'.
We have upgraded to the latest Apache Beam version as well as the Iceberg core library, but the issue persists.

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Reminder, please take a look at this pr: @robertwb

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Reminder, please take a look at this pr: @chamikaramj

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[ahmedabu98]

hey @mskyrim, can you please run iceberg integration tests on this PR? just modify this file and commit a change: https://github.com/apache/beam/blob/master/.github/trigger_files/IO_Iceberg_Integration_Tests.json

[mskyrim]

Hi @ahmedabu98
i have modified the file here is the pull request
#36807

[ahmedabu98]

@mskyrim please modify it directly in this PR so the tests can run against these changes.

[mskyrim]

done @ahmedabu98

[ahmedabu98]

Looks good, thanks for fixing this @mskyrim!