[goutamabrol]

Adds the Japan_Census import under statvar_imports/japan_census/ for Japan Population Census, Employment, Education, Mortality, and Health Statistics from the Official Statistics of Japan (e-Stat).

• Data Source: Portal Site of Official Statistics of Japan (e-Stat Statistical Dashboard JSON API https://dashboard.e-stat.go.jp/api/1.0/Json/getData), covering National (country/JPN), 47 Prefectures (AdministrativeArea1), and 1,917 Municipalities (AdministrativeArea2) across census waves (1920–2025) and annual statistical releases (1948–2026).
• Coverage: Maps 101 canonical StatVars across demographics (total population and 5-year/broad age brackets by gender), labor force (employment, unemployment, not in labor force, unemployment rate), education (students and teachers by school level), and vital/health statistics (deaths by gender and cause of death), generating 296,108 observations from 415,244 raw records (+27,760 new 2022–2026 observations added, 0 deleted, 0 modified vs. previous Japan_Census import).
• Downloader & Processor (download_script.py, process.py, & unit tests): Downloads all 9 dataset groups in parallel from the e-Stat JSON API, derives broad age-group totals (<15, 15–64, 65+, 85+), merges pre-1975/archival historical records from gs://unresolved_mcf/country/japan/deleted_historical_data.csv with atomic file writes into 18 input CSVs, and processes shards concurrently via process.py.
• Mappings: Unified PV map (japan_census_pv_map.csv) and metadata config (japan_census_metadata.csv) mapping year, indicatorCd, regionCd, and value across all 1,965 places (country/JPN and wikidataId/Q...), scaling labor force counts (#Multiply,10) to match existing scaling factors, and filtering non-target regional aggregate rows via #IgnoreRow.
• Automation (manifest.json): Configured for Cloud Batch execution with download_script.py, process.py (--existing_statvar_mcf, --output_counters, node_mcf), and automated monthly cron schedule (0 5 1 * *).
• Validation (validation_config.json): Enforces historical deletion threshold of 0.1% (DELETED_RECORDS_PERCENT) and date freshness/value bounds (SQL_VALIDATOR) across all 92 active recurring StatVars and 9 historical centenarian sub-brackets (100–104, 105–109, 110+).

Cloud Batch Verified: End-to-end job completed with status SUCCEEDED.

PR Checklist: link

Cloud Batch Job (test) - link

Validation: link

[gemini-code-assist]

Code Review

This pull request introduces an automated import pipeline for Japan Census and Demographic Statistics, including scripts for downloading data from the e-Stat API and a parallel processing wrapper to merge the resulting datasets. The feedback focuses on improving process.py by replacing ProcessPoolExecutor with ThreadPoolExecutor for I/O-bound subprocess tasks, adding explicit checks for empty input directories to raise a FileNotFoundError, and cleaning up standard library imports by moving tempfile to the top of the file.