This function retrieves the active DuckLake connection. If no connection
has been explicitly set via set_ducklake_connection(), it falls back
to duckplyr's default DuckDB connection for seamless integration.
Note
This function uses duckplyr:::get_default_duckdb_connection()
as a fallback when no connection has been explicitly set. While this accesses
an unexported function, it is necessary for proper duckplyr integration as
duckplyr's connection provides critical setup (singleton pattern, temp directory
configuration, R function loading, and macro registration) that cannot be
easily replicated. See the duckplyr source for details:
https://github.com/tidyverse/duckplyr/blob/main/R/relational-duckdb.R