refactor: split base_cost.rs into multiple files (#156)

Move cost model code to separate files.

- Statistics generation -> `src/cost/base_cost/stats.rs`
- Filter selectivity -> `src/cost/base_cost/filter.rs`
- Join selectivity -> `src/cost/base_cost/join.rs`
- Limit cardinality -> `src/cost/base_cost/limit.rs`
- Agg cardinality -> `src/cost/base_cost/agg.rs`

Author: Gun9niR

optd-datafusion-repr/src/bin/test_optimize.rs

@@ -8,7 +8,7 @@ use optd_core::{
     rules::{Rule, RuleWrapper},
 };
 use optd_datafusion_repr::{
-    cost::{base_cost::DataFusionPerTableStats, OptCostModel},
+    cost::{DataFusionPerTableStats, OptCostModel},
     plan_nodes::{
         BinOpExpr, BinOpType, ColumnRefExpr, ConstantExpr, JoinType, LogicalFilter, LogicalJoin,
         LogicalScan, OptRelNode, OptRelNodeTyp, PlanNode,

optd-datafusion-repr/src/cost.rs

@@ -1,11 +1,9 @@
 pub mod adaptive_cost;
 pub mod base_cost;
-mod stats;
 
 pub use adaptive_cost::{AdaptiveCostModel, RuntimeAdaptionStorage, DEFAULT_DECAY};
-pub use base_cost::{
-    BaseTableStats, OptCostModel, PerColumnStats, PerTableStats, COMPUTE_COST, IO_COST, ROW_COUNT,
-};
+pub use base_cost::stats::{BaseTableStats, DataFusionBaseTableStats, DataFusionPerTableStats};
+pub use base_cost::{OptCostModel, COMPUTE_COST, IO_COST, ROW_COUNT};
 
 pub trait WithRuntimeStatistics {
     fn get_runtime_statistics(&self) -> RuntimeAdaptionStorage;

optd-datafusion-repr/src/cost/adaptive_cost.rs

@@ -10,7 +10,7 @@ use optd_core::{
     rel_node::{RelNode, Value},
 };
 
-use super::base_cost::{
+use super::base_cost::stats::{
     BaseTableStats, DataFusionDistribution, DataFusionMostCommonValues, Distribution,
     MostCommonValues,
 };