Add timezone support for date calculation in TimeSensor

[SML0127]

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This PR closes #38337

In the previous logic (using datetime.datetime.today()), if server's timezone is UTC, target_datetime for TimeSensor could be incorrectly.

For example, when the user intended to use Asia/Singapore timezone and server timezone is UTC, taget time 2025-01-27 07:00:00+08:00 might be incorrectly converted to 2025-01-25 23:00:00 UTC instead of 2025-01-26 23:00:00 UTC.
(This assumes the current time is 2025-01-26 23:00:00 UTC, which is 2025-01-27 07:00:00 in Asia/Singapore.)

This happens because the local date 2025-01-26 is combined with the target time 07:00:00, resulting in 2025-01-26 07:00:00 in local time. And then this datetime is converted to UTC using convert_to_utc, it becomes 2025-01-25 23:00:00 UTC.

To fix this, pendulum.now(tz=str(self.dag.timezone)) is used instead of datetime.datetime.today().

All unit tests for TimeSensor passed

[boring-cyborg]

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[SML0127]

@uranusjr Thank you for the kind and detiled comments. I've addressed the points you mentioned.

[SML0127]

@uranusjr Thank you for the kind and detiled comments. I've addressed the points you mentioned.

unit test results

[boring-cyborg]

Awesome work, congrats on your first merged pull request! You are invited to check our Issue Tracker for additional contributions.

[dwreeves]

Thank you for resolving the issue! ❤️