Add sink before recursive join

[andyfengHKU]

This is to achieve better granularity for SSP computation. This sink is also needed for a different parallelism strategy where multiple threads can work on a single source.

[codecov]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (d9695fd) 92.27% compared to head (ddfdcde) 92.27%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1500   +/-   ##
=======================================
  Coverage   92.27%   92.27%           
=======================================
  Files         675      675           
  Lines       24264    24275   +11     
=======================================
+ Hits        22389    22400   +11     
  Misses       1875     1875           

Impacted Files	Coverage Δ
...cessor/operator/var_length_extend/recursive_join.h	100.00% <100.00%> (ø)
src/planner/join_order/cardinality_estimator.cpp	96.55% <100.00%> (-0.06%)	⬇️
src/planner/operator/logical_recursive_extend.cpp	100.00% <100.00%> (ø)
src/processor/mapper/map_extend.cpp	95.23% <100.00%> (+0.36%)	⬆️
...ssor/operator/var_length_extend/recursive_join.cpp	98.61% <100.00%> (+0.10%)	⬆️

☔ View full report in Codecov by Sentry.
📢 Do you have feedback about the report comment? Let us know in this issue.