Eliminate unary plus from AST (no-op in ClickHouse) (#122)

In ClickHouse, unary plus (+x) is a no-op and doesn't appear in the
EXPLAIN AST output. Updated parseUnaryPlus to simply return the
operand without wrapping it in a UnaryExpr.

This fixes parsing of expressions like (+c0.2) which should produce
just tupleElement, not Function + wrapping tupleElement.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: kyleconroy

parser/expression.go

@@ -1167,13 +1167,9 @@ func (p *Parser) parseUnaryPlus() ast.Expression {
 		}
 	}
 
-	// Standard unary plus handling
-	expr := &ast.UnaryExpr{
-		Position: pos,
-		Op:       "+",
-	}
-	expr.Operand = p.parseExpression(UNARY)
-	return expr
+	// In ClickHouse, unary plus is a no-op and doesn't appear in EXPLAIN AST.
+	// Simply return the operand without wrapping it in UnaryExpr.
+	return p.parseExpression(UNARY)
 }
 
 func (p *Parser) parseNot() ast.Expression {

parser/testdata/01764_collapsing_merge_adaptive_granularity/metadata.json

@@ -1,5 +1 @@
-{
-  "explain_todo": {
-    "stmt4": true
-  }
-}
+{}

parser/testdata/03207_json_read_subcolumns_1_memory/metadata.json

@@ -1,5 +1 @@
-{
-  "explain_todo": {
-    "stmt14": true
-  }
-}
+{}

parser/testdata/03207_json_read_subcolumns_2_memory/metadata.json

@@ -1,5 +1 @@
-{
-  "explain_todo": {
-    "stmt14": true
-  }
-}
+{}

parser/testdata/03720_file_engine_second_crash/metadata.json

@@ -1,5 +1 @@
-{
-  "explain_todo": {
-    "stmt1": true
-  }
-}
+{}