Added goldens for USCensuspep imports

[niveditasing]

Overview
This PR updates the Python preprocessing and ingestion scripts across PEP (Population Estimates Program) datasets to ensure compatibility
with Pandas 2.0+ and optimize processing logic.

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1. Pandas Compatibility Updates

• Replaced Deprecated delim_whitespace: Replaced delim_whitespace=True with sep=r'\s+' inside pd.read_table() calls to support modern
  Pandas versions in:
  • monthly_population_estimate/preprocess.py
  • population_estimates_by_asr/ (county, national, and state scripts)
  • us_pep_sex/process.py
  • us_pep_sexrace/ (county, national, and state scripts)
• Replaced Direct Indexing: Replaced index-based Series access (e.g., col[0]) with explicit .iloc indexer (col.iloc[0]) in
  monthly_population_estimate/preprocess.py

2. Added golden to all these 4 Directories

[gemini-code-assist]

Code Review

This pull request introduces validation configurations, golden summary reports, and generated outputs for the US Census PEP monthly population estimate and sex datasets. Additionally, it updates download routines in process.py to include timeouts, retries with exponential backoff, and sorted file processing. Feedback on the changes highlights an incorrect golden file path in the us_pep_sex validation configuration and a potential resource leak in process.py where temporary files are not cleaned up if an exception occurs during file copy or move operations.