[BSE-4469] Split Iceberg IO Code into Multiple Files

[srilman]

Changes included in this PR

Split the Bodo-side Python code for reading and writing Iceberg tables into multiple files in anticipation of adding the PyIceberg integration.

Testing strategy

Running PR Ci and Nightly with the Iceberg flag.

User facing changes

Internal changes only

Checklist

• Pipelines passed before requesting review. To run CI you must include [run CI] in your commit message.
• I am familiar with the Contributing Guide
• I have installed + ran pre-commit hooks.

[codecov]

Codecov Report

Attention: Patch coverage is 67.47529% with 362 lines in your changes missing coverage. Please review.

Please upload report for BASE (main@bb0bdb3). Learn more about missing BASE report.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #130   +/-   ##
=======================================
  Coverage        ?   77.94%           
=======================================
  Files           ?      169           
  Lines           ?    62085           
  Branches        ?     8722           
=======================================
  Hits            ?    48393           
  Misses          ?    11579           
  Partials        ?     2113