[Kayvan-Zahiri]

Naive datetimes in call-history filters receive today's local UTC offset, shifting historical/future filter boundaries across DST seasons. In Los Angeles during PDT, January noon is sent with -07:00 rather than -08:00.

Use the input datetime's astimezone() conversion to apply local rules for its own date, including ambiguous fall-back folds. Explicitly aware datetimes retain existing behavior.

Fixes #29. This is a tested proof of concept under the README contribution policy: the change belongs in the Fern-generated runtime and needs porting into generation before durable merge.

Validation:

• 56 new public sync/async calls.list HTTPX MockTransport cases cover four created/updated filters, winter/summer, both DST folds, explicit UTC/positive-offset datetimes, and microseconds. Before: 24 failed, 32 passed. After: all 56 pass.
• Full repository suite: 135 passed, 4 skipped, 326 existing Pydantic deprecation warnings.
• Changed-file Ruff lint/format, targeted mypy, and git diff --check pass. Repository-wide Ruff reports three pre-existing import-order errors in unchanged custom test files.
• Tests restore TZ after every case and skip runtime timezone switching on platforms without time.tzset. No live voice calls, credentials, or paid Vapi resources used.