feat(duckdb): Add transpilation support for Snowflake STARTS WITH

[fivetran-kwoodbeck]

Adds Snowflake to DuckDB transpilation for START WITH ... CONNECT BY PRIOR hierarchical queries.

DuckDB rejects CONNECT BY verbatim. This adds connect_by_to_recursive_cte registered as a preprocessor on exp.Select, which rewrites the query into a WITH RECURSIVE CTE at generation time:

• Anchors START WITH rows from the source table
• Recursive arm: source table aliased _child_row joined to the CTE aliased _parent_row on the PRIOR predicate
• Outer SELECT re-projects from _rootcte, applying WHERE post-hierarchy and forwarding ORDER BY, LIMIT, OFFSET

Falls through unchanged for NOCYCLE, multiple PRIORs, or non-equality predicates. CTE name collision is avoided via find_new_name. WHERE columns absent from SELECT are carried through the CTE so the outer filter can see them. LEVEL is injected as a depth counter unless already projected.

Tests in sqlglot-integration-tests cover: SELECT *, explicit column list with ORDER BY, PRIOR on left side, WHERE carry-through, existing CTE preservation, and name collision.

[github-actions]

SQLGlot Integration Test Results

✅ All tests passed

Comparing:

• this branch (sqlglot:transpile/snowflake-startswith @ sqlglot 601a4bd)
• baseline (main @ sqlglot 6ae53c2)

Overall

main: 113231 total, 112182 passed (pass rate: 99.1%)

sqlglot:transpile/snowflake-startswith: 106860 total, 106860 passed (pass rate: 100.0%)

Transitions:
No change

Dialect pair changes: 0 previous results not found, 2 current results not found

✅ All tests passed