fix: limit row cnt

[Gun9niR]

Change the LIMIT output cardinality to min(child, fetch). In the below, I hard-coded PhysicalScan's cardinality to 10, because cli does not support stats yet.

❯     create table t1(v1 int);

0 rows in set. Query took 0.011 seconds.

Execution took 0.000 secs, Planning took 0.000 secs
❯     insert into t1 values (0), (1), (2), (3);

❯ explain verbose select * from t1 limit 2;
+--------------------------------------------------+-------------------------------------------------------------------------------------------------+
| plan_type                                        | plan                                                                                            |
+--------------------------------------------------+-------------------------------------------------------------------------------------------------+
| logical_plan after datafusion                    | Limit: skip=0, fetch=2                                                                          |
|                                                  |   Projection: t1.v1                                                                             |
|                                                  |     TableScan: t1                                                                               |
| logical_plan after optd                          | LogicalLimit { skip: 0, fetch: 2 }                                                              |
|                                                  | └── LogicalProjection { exprs: [ #0 ] }                                                         |
|                                                  |     └── LogicalScan { table: t1 }                                                               |
| physical_plan after optd                         | PhysicalLimit { skip: 0, fetch: 2, cost: weighted=3.12,row_cnt=1.00,compute=2.12,io=1.00 }      |
|                                                  | └── PhysicalProjection { exprs: [ #0 ], cost: weighted=1.06,row_cnt=1.00,compute=0.06,io=1.00 } |
|                                                  |     └── PhysicalScan { table: t1, cost: weighted=1.00,row_cnt=1.00,compute=0.00,io=1.00 }       |
| physical_plan after optd-join-order              | t1                                                                                              |
| physical_plan after optd-all-join-orders         | SAME TEXT AS ABOVE                                                                              |
| physical_plan after optd-all-logical-join-orders | SAME TEXT AS ABOVE                                                                              |
| physical_plan                                    | GlobalLimitExec: skip=0, fetch=2                                                                |
|                                                  |   ProjectionExec: expr=[<expr>@0 as col0]                                                       |
|                                                  |     MemoryExec: partitions=1, partition_sizes=[1]                                               |
|                                                  |                                                                                                 |
+--------------------------------------------------+-------------------------------------------------------------------------------------------------+

[wangpatrick57]

LGTM