Extend SQL pushdown: multi-hop, filters, aggregation, ORDER BY, recursive CTE

[adsharma]

Stacked on the DuckLake pushdown series (first three commits below belong to it; this PR's change is the last commit: 83dc796ac).

SQL pushdown previously fired only for a narrow set of 1-hop star patterns (and, due to a null referencedEntry in the DuckDB catalog — fixed in LadybugDB/extensions#88 — often not even then). This PR generalizes ForeignJoinPushDownOptimizer:

• N-hop chain matching: collects EXTEND hops, foreign node scans and FILTER predicates from hash-join subtrees regardless of nesting, emitting one multi-way SQL JOIN (BFS order; extra ON conjuncts for already-bound neighbours, so cycles/diamonds stay correct). Node/edge filters re-attach above the pushed scan and fold into SQL WHERE via filter pushdown.
• Aggregation pushdown: supported AGGREGATEs (COUNT/SUM/AVG/MIN/MAX) fold into GROUP BY; kept projection spines are expanded so projection pushdown cannot prune grouped columns.
• ORDER BY pushdown: sort keys fold into pushed scans; order-by pushdown now resolves keys against scan output aliases, goes all-or-nothing, and never drops an ORDER BY it could not push (previously an untranslatable key silently lost the sort — wrong results).
• Recursive CTE: variable-length patterns matched top-down along the root spine (WALK, finite bound, directed) rewrite to WITH RECURSIVE; inline edge predicates bake into anchor + recursive member; path/shortest-path cases stay local.

Planner hardening so foreign variable-length patterns plan at all: the cardinality estimator skips non-lbug attached entries instead of downcasting them to AttachedLbugDatabase (UB/crash), and recursive rel-property scans tolerate foreign rels without an internal _ID.

Requires LadybugDB/extensions#88 for end-to-end pushdown over DuckDB-attached tables (engine changes alone are inert and covered by native suites). The submodule pointer bump follows once #88 merges.

Verification done locally: 1-hop/2-hop/filter/agg/order/recursive result matrices over an attached DuckDB graph (mirrored in sql_pushdown.test in #88); c_api_test 146 passed; e2e order/limit/aggregate (53), graph/attach/path (37) green (one pre-existing failure from a missing parquet fixture, unrelated).

CI: run the rest on CI (full e2e + extension-test trees).