Normalize timestamps by stripping time zone offsets from Health data

[Polumm]

Summary

This PR introduces a minimal, backwards-compatible patch to normalize Apple Health timestamps by stripping time zone offsets. It ensures compatibility with SQL TIMESTAMP WITHOUT TIME ZONE fields and resolves import issues on newer iOS exports (e.g., June 2025).

Changes

• ✅ Added _strip_tz() helper in parse.py to clean creationDate, startDate, and endDate values
• ✅ Updated parse.py to use the helper in the default record stream
• ✅ Updated ActivitySummaryFormatter and SleepAnalysisFormatter in formatters.py to apply the same normalization
• ✅ Handles malformed timestamps gracefully (logged and passed through)

Motivation

iOS-exported data may include time zone offsets (e.g., +0100), which are incompatible with the current database schema. This fix ensures consistent ingestion across older and newer data sets.