[Refactor] use new model.batch context vars

[MichelleArk]

resolves #1263
docs dbt-labs/docs.getdbt.com/#

Problem

With the introduction of the new batch context variable in dbt-core==1.9.0rc2, it is recommended to use batch.event_time_start and batch.event_time_end over node.config.__dbt_internal.* variables.

Solution

copy+replace, with safe access of model.batch property

Checklist

• I have read the contributing guide and understand what's expected of me
• I have run this code in development and it appears to resolve the stated issue
• This PR includes tests, or tests are not required/relevant for this PR
• This PR has no interface changes (e.g. macros, cli, logs, json artifacts, config files, adapter interface, etc) or this PR has already received feedback and approval from Product or DX

[github-actions]

Thank you for your pull request! We could not find a changelog entry for this change. For details on how to document a change, see the dbt-snowflake contributing guide.

[github-actions]

Thank you for your pull request! We could not find a changelog entry for this change. For details on how to document a change, see the dbt-snowflake contributing guide.

[QMalcolm]

I have one concern about the new pattern 🤔

[QMalcolm]

🚀