fix(cdk): replace direct datetime parsing/formatting with datetime_helpers (do not merge)

[devin-ai-integration]

This PR replaces direct datetime parsing and formatting with standardized implementations from the datetime_helpers module as documented in the Airbyte Python CDK documentation. It also fixes a bug in ab_datetime_format() where it doesn't respect the requested format when an AirbyteDateTime object is passed.

Link to Devin run: https://app.devin.ai/sessions/dc992333d5b04a3cb9aed7db246b30de

Requested by: Aaron ("AJ") Steers ([email protected])

[devin-ai-integration]

Original prompt from Aaron:

@Devin - I want you to make a pass through the CDK and find/replace references of direct datetime parsing and datetime formatting. Replace with the implementation as documented here: <https://airbytehq.github.io/airbyte-python-cdk/airbyte_cdk/utils/datetime_helpers.html>

[devin-ai-integration]

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[devin-ai-integration]

Closing due to inactivity for more than 7 days.