fix: missing metadata handling in is_hudi and is_iceberg

[aarushisingh04]

description

can_be_replaced calls is_iceberg without first checking whether metadata is available. on relations that haven't fetched extended metadata yet (metadata=None) this hits an unconditional assert self.metadata is not None and crashes the dbt run with an AssertionError.

the fix

• updates is_hudi and is_iceberg to safely return False when self.metadata is None, making their behavior consistent with other metadata properties like owner and stats.
• unit tests have also been added to ensure properties evaluate gracefully on un-hydrated relations.

checklist

• 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
• I have updated the CHANGELOG.md and added information about my change to the "dbt-databricks next" section.