fix(charts): handle PostgreSQL INTERVAL type in bar and pie charts

PostgreSQL INTERVAL types were causing bar and pie charts to fail rendering when used as metrics. This fix converts INTERVAL values (timedelta objects) to numeric seconds so they can be properly displayed in charts.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

tests/unit_tests/db_engine_specs/test_postgres.py

@@ -15,14 +15,14 @@
 # specific language governing permissions and limitations
 # under the License.
 
-from datetime import datetime
+from datetime import datetime, timedelta
 from typing import Any, Optional
 from unittest.mock import MagicMock
 
 import pytest
 from pytest_mock import MockerFixture
 from sqlalchemy import column, types
-from sqlalchemy.dialects.postgresql import DOUBLE_PRECISION, ENUM, JSON
+from sqlalchemy.dialects.postgresql import DOUBLE_PRECISION, ENUM, INTERVAL, JSON
 from sqlalchemy.engine.interfaces import Dialect
 from sqlalchemy.engine.url import make_url
 
@@ -363,3 +363,18 @@ class TestRedshiftDetection:
         spec.update_params_from_encrypted_extra(database, params)
 
         assert "pool_events" not in params
+
+
+def test_interval_type_mutator() -> None:
+    """
+    DB Eng Specs (postgres): Test INTERVAL type mutator
+    """
+    # Test timedelta conversion
+    td = timedelta(days=1, hours=2, minutes=30, seconds=45)
+    mutator = spec.column_type_mutators[INTERVAL]
+    assert mutator(td) == 95445.0  # Total seconds: 1*86400 + 2*3600 + 30*60 + 45
+
+    # Test that non-timedelta values pass through unchanged
+    assert mutator("not a timedelta") == "not a timedelta"
+    assert mutator(12345) == 12345
+    assert mutator(None) is None