python(fix): infer parquet time column for int64/uint64 timestamps

[wei-qlu]

Summary

• This adds a client-side fallback that picks the first INT64 or UINT64 column whose name (case-insensitive) is ts, timestamp, or time and removes it from data_columns.
• Applies to both PARQUET_FLATDATASET and PARQUET_SINGLE_CHANNEL_PER_ROW layouts.

Test plan

• Unit tests: pytest python/lib/sift_client/_tests/resources/test_data_imports.py
• Import a Parquet file with a bare int64 timestamp column via client.data_imports.import_from_path(...) and confirm the returned config promotes it to time_column and excludes it from data_columns.
• Import a Parquet file whose timestamp uses Arrow timestamp(ns) and confirm server-side detection still wins (no regression).

[github-actions]

Python docs preview: https://sift-stack.github.io/sift/python/pr-582/

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