feat: add named secret support DuckDB

[eakmanrq]

Prior to this PR, users were forced to use the default secret name when creating secrets. Now they can still do that or create secrets with a specific name. This is required to support a use case where users want to define multiple secrets for a single type (ex: multiple secrets for S3) since before they would get an error saying the default name was already defined.

[Copilot]

Pull Request Overview

Adds support for named secrets in DuckDB connections, allowing multiple secrets per connection either as a list or a dict with custom names.

• Extends the secrets config type and initialization to handle dict-based named secrets.
• Updates tests to cover both list and dict formats for DuckDB secrets.
• Revises examples and documentation to illustrate named and default secret usage.

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
tests/core/test_connection_config.py	Added tests for multiple and named DuckDB secrets
sqlmesh/core/config/connection.py	Changed secrets field type and init logic for naming
examples/sushi/config.py	Updated example to show named secret configuration
docs/integrations/engines/duckdb.md	Expanded docs with list vs. dict formats for secrets

Comments suppressed due to low confidence (3)

tests/core/test_connection_config.py:7

• The test uses call in assertions but does not import it from unittest.mock; add call to the import to avoid a NameError.

from unittest.mock import patch, MagicMock

sqlmesh/core/config/connection.py:280

• Using a mutable default for the secrets field can lead to shared state issues; consider using Field(default_factory=list) (or equivalent) for list defaults or default_factory=dict when appropriate.

    secrets: t.Union[t.List[t.Dict[str, t.Any]], t.Dict[str, t.Dict[str, t.Any]]] = []

sqlmesh/core/config/connection.py:380

• [nitpick] When secret_name is empty, this generates an extra space in the SQL (CREATE SECRET ...); consider conditionally adding the space only when a name is provided.

                                cursor.execute(f"CREATE SECRET {secret_name} ({secret_clause});")

[eakmanrq]

This is a typo I found while reviewing the docs after the change in this PR