fix(query): use jiff to_zoned for naive datetime timezone resolution

[TCeason]

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Summary

string_to_timestamp_tz used a "fake UTC" approach to resolve timezone
offset for naive datetime inputs: it treated the naive datetime as UTC,
then looked up the timezone offset at that (wrong) UTC instant. This
produced incorrect results when the fake and real UTC instants straddled
a DST transition.

For example, '2024-11-03 05:30:00' in America/New_York should resolve
to EST (-0500), giving real UTC 10:30. But the old code treated 05:30
as UTC to look up the offset, and since 05:30 UTC is before the 06:00
UTC transition, it got EDT (-0400) instead of EST (-0500).

Fix: replace the manual fake-UTC-then-lookup with jiff's
DateTime::to_zoned(), which correctly interprets a naive datetime in
the target timezone and handles DST disambiguation natively.

Tests

• Unit Test
• Logic Test
• Benchmark Test
• No Test - Explain why

Type of change

• Bug Fix (non-breaking change which fixes an issue)
• New Feature (non-breaking change which adds functionality)
• Breaking Change (fix or feature that could cause existing functionality not to work as expected)
• Documentation Update
• Refactoring
• Performance Improvement
• Other (please describe):

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