refactor: unify expression and operator traversal with visitors

[KKould]

What problem does this PR solve?

Expression and operator traversal was duplicated across binders and optimizer rules, making new operator variants easy to miss and error propagation inconsistent.

Issue link: N/A

What is changed and how it works?

• Rename the expression visitor traits to ExprVisitor and ExprVisitorMut.
• Add decoupled OperatorVisitor and OperatorVisitorMut traits for operator dispatch.
• Add concrete OperatorExprVisitor and OperatorExprVisitorMut adapters for traversing expressions embedded in operators.
• Replace manual operator-expression traversal in evaluator binding, constant calculation, column pruning, and related binder/optimizer paths.
• Propagate DatabaseError through referenced-column and expression inspection APIs.
• Simplify predicate pushdown classification without intermediate partition vectors.
• Add edge-case, visitor, parameterized-index, operator, and binder E2E coverage tests.

Code changes

• Has Rust code change
• Has CI related scripts change

Check List

Tests

• Unit test
• Integration test
• Manual test (make test-all, make codecov, and strict Clippy)
• No code

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

[codecov]

Codecov Report

❌ Patch coverage is 96.93815% with 50 lines in your changes missing coverage. Please review.
✅ Project coverage is 92.74%. Comparing base (a28b4ab) to head (498d051).

Files with missing lines	Patch %	Lines
src/optimizer/rule/normalization/column_pruning.rs	84.54%	17 Missing ⚠️
src/binder/select.rs	84.31%	8 Missing ⚠️
src/planner/operator/visitor.rs	98.87%	5 Missing ⚠️
...mizer/rule/normalization/compilation_in_advance.rs	96.72%	4 Missing ⚠️
src/planner/operator/mod.rs	97.20%	4 Missing ⚠️
...ptimizer/rule/normalization/pushdown_predicates.rs	97.16%	3 Missing ⚠️
src/db.rs	75.00%	2 Missing ⚠️
src/optimizer/rule/normalization/elimination.rs	93.33%	2 Missing ⚠️
...ptimizer/rule/normalization/parameterized_index.rs	93.54%	2 Missing ⚠️
src/serdes/data_value.rs	96.66%	2 Missing ⚠️
... and 1 more

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #372      +/-   ##
==========================================
+ Coverage   92.09%   92.74%   +0.64%     
==========================================
  Files         241      243       +2     
  Lines       39870    41025    +1155     
==========================================
+ Hits        36720    38049    +1329     
+ Misses       3150     2976     -174     

Flag	Coverage Δ
rust	92.74% <96.93%> (+0.64%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
src/binder/aggregate.rs	97.59% <100.00%> (ø)
src/binder/distinct.rs	98.47% <ø> (ø)
src/binder/parser.rs	86.96% <100.00%> (ø)
src/catalog/column.rs	95.70% <100.00%> (ø)
src/catalog/view.rs	94.44% <100.00%> (+1.58%)	⬆️
src/expression/mod.rs	84.93% <100.00%> (ø)
src/expression/range_detacher.rs	93.64% <100.00%> (+0.29%)	⬆️
src/expression/simplify.rs	87.44% <ø> (ø)
src/expression/visitor.rs	92.65% <100.00%> (ø)
src/expression/visitor_mut.rs	93.64% <100.00%> (ø)
... and 18 more

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