Add input validation to ExecutorConfigType bind and result processors

[Atharva2012]

Add input validation to ExecutorConfigType bind and result processors

ExecutorConfigType.bind_processor and result_processor did not validate their inputs. Passing a non-dict value would silently bypass the pod_override logic and either store unexpected data in the DB (on write) or return incorrect data (on read), with no helpful error message.
This PR adds:

• A None early-return in both processors (NULL is valid for DB columns)

• A TypeError with a descriptive message when the value is not a dict

• Tests covering both valid and invalid inputs for both processors

closes: #69011

Was generative AI tooling used to co-author this PR?

• Yes (please specify the tool below)
  Claude, to help word this PR and to navigate the codebase

[boring-cyborg]

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[Atharva2012]

This is my first contribution to airflow, have been using it or a while. Happy to address any feedback.
Thank you

[Atharva2012]

Closing this as the related issue was marked not planned. Happy to revisit if members see any value in this direction.