perf: skip unnecessary metadata fetch calls for tags when not configured

[tejassp-db]

Summary

• Skips fetch_tags and fetch_column_tags queries to information_schema during incremental and view materializations when the model has no tags configured
• Falls back to fetching metadata when model config is unavailable (safe default)
• No behavior change for models with tags configured — diffs still computed correctly

What changed

• Added requires_server_metadata_for_diff() to TagsConfig and ColumnTagsConfig to signal when server metadata is needed
• IncrementalTableAPI._describe_relation and ViewAPI._describe_relation now check model config before making tag fetch calls
• get_relation_config accepts the model config to pass through to _describe_relation
• Fixed duplicate TagsProcessor in StreamingTableConfig.config_components

Test plan

• Unit tests: empty tags (skip), non-empty tags (fetch), null config fallback (fetch), both tags + column tags present, hive_metastore (skip)

• Functional tests: override fetch_tags/fetch_column_tags macros to raise errors, confirming calls are actually skipped when expected

  PECOBLR-2497

[github-actions]

Coverage report

Click to see where and how coverage changed

File	Statements	Missing	Coverage	Coverage (new stmts)	Lines missing
dbt/adapters/databricks
impl.py					931, 935-944, 1027-1029, 1054-1057, 1076-1077, 1101-1102
dbt/adapters/databricks/relation_configs
base.py					41
column_tags.py
tags.py
Project Total

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