refactor: move COALESCE into Conditional namespace

- Renamed CoalesceFunction → Conditional.Coalesce
- Maintains all existing functionality:
  - ?? operator overloads for query expressions
  - .ifnull() extension methods
  - Deprecated operator warnings for non-optional types
- Follows namespace pattern: COALESCE is a conditional expression (PostgreSQL §9.18)
- File renamed: Coalesce.swift → Conditional.Coalesce.swift

Pattern: Semantic grouping by PostgreSQL documentation structure

Author: coenttb

…res/Functions/Conditional/Coalesce.swift …s/Conditional/Conditional.Coalesce.swiftSources/StructuredQueriesPostgres/Functions/Conditional/Coalesce.swift renamed to Sources/StructuredQueriesPostgres/Functions/Conditional/Conditional.Coalesce.swift Sources/StructuredQueriesPostgres/Functions/Conditional/Coalesce.swift renamed to Sources/StructuredQueriesPostgres/Functions/Conditional/Conditional.Coalesce.swift

@@ -8,35 +8,37 @@ import StructuredQueriesCore
 //
 // COALESCE returns the first non-NULL value from its arguments.
 
-/// A query expression of a coalesce function.
-///
-/// Represents PostgreSQL's `COALESCE` function which returns the first non-NULL value.
-/// This is used to implement Swift's `??` operator for query expressions.
-///
-/// ```swift
-/// User.select { $0.nickname ?? $0.name }
-/// // SELECT coalesce("users"."nickname", "users"."name") FROM "users"
-/// ```
-public struct CoalesceFunction<QueryValue>: QueryExpression {
-    private let arguments: [QueryFragment]
+extension Conditional {
+    /// A query expression of a COALESCE function.
+    ///
+    /// Represents PostgreSQL's `COALESCE` function which returns the first non-NULL value.
+    /// This is used to implement Swift's `??` operator for query expressions.
+    ///
+    /// ```swift
+    /// User.select { $0.nickname ?? $0.name }
+    /// // SELECT coalesce("users"."nickname", "users"."name") FROM "users"
+    /// ```
+    public struct Coalesce<QueryValue>: QueryExpression {
+        private let arguments: [QueryFragment]
 
-    fileprivate init(_ arguments: [QueryFragment]) {
-        self.arguments = arguments
-    }
+        fileprivate init(_ arguments: [QueryFragment]) {
+            self.arguments = arguments
+        }
 
-    public var queryFragment: QueryFragment {
-        "coalesce(\(arguments.joined(separator: ", ")))"
-    }
+        public var queryFragment: QueryFragment {
+            "coalesce(\(arguments.joined(separator: ", ")))"
+        }
 
-    public static func ?? <T: _OptionalProtocol<QueryValue>>(
-        lhs: some QueryExpression<T>,
-        rhs: Self
-    ) -> CoalesceFunction<QueryValue> {
-        Self([lhs.queryFragment] + rhs.arguments)
+        public static func ?? <T: _OptionalProtocol<QueryValue>>(
+            lhs: some QueryExpression<T>,
+            rhs: Self
+        ) -> Coalesce<QueryValue> {
+            Self([lhs.queryFragment] + rhs.arguments)
+        }
     }
 }
 
-extension CoalesceFunction where QueryValue: _OptionalProtocol {
+extension Conditional.Coalesce where QueryValue: _OptionalProtocol {
     public static func ?? (
         lhs: some QueryExpression<QueryValue>,
         rhs: Self
@@ -104,8 +106,8 @@ extension QueryExpression where QueryValue: _OptionalProtocol {
     public static func ?? (
         lhs: Self,
         rhs: some QueryExpression<QueryValue.Wrapped>
-    ) -> CoalesceFunction<QueryValue.Wrapped> {
-        CoalesceFunction([lhs.queryFragment, rhs.queryFragment])
+    ) -> Conditional.Coalesce<QueryValue.Wrapped> {
+        Conditional.Coalesce([lhs.queryFragment, rhs.queryFragment])
     }
 
     /// Applies each side of the operator to the `coalesce` function
@@ -126,8 +128,8 @@ extension QueryExpression where QueryValue: _OptionalProtocol {
     public static func ?? (
         lhs: Self,
         rhs: some QueryExpression<QueryValue>
-    ) -> CoalesceFunction<QueryValue> {
-        CoalesceFunction([lhs.queryFragment, rhs.queryFragment])
+    ) -> Conditional.Coalesce<QueryValue> {
+        Conditional.Coalesce([lhs.queryFragment, rhs.queryFragment])
     }
 
     @_documentation(visibility: private)
@@ -140,8 +142,8 @@ extension QueryExpression where QueryValue: _OptionalProtocol {
     public static func ?? (
         lhs: some QueryExpression<QueryValue.Wrapped>,
         rhs: Self
-    ) -> CoalesceFunction<QueryValue> {
-        CoalesceFunction([lhs.queryFragment, rhs.queryFragment])
+    ) -> Conditional.Coalesce<QueryValue> {
+        Conditional.Coalesce([lhs.queryFragment, rhs.queryFragment])
     }
 }
 
@@ -156,7 +158,7 @@ extension QueryExpression {
     public static func ?? (
         lhs: some QueryExpression<QueryValue>,
         rhs: Self
-    ) -> CoalesceFunction<QueryValue> {
-        CoalesceFunction([lhs.queryFragment, rhs.queryFragment])
+    ) -> Conditional.Coalesce<QueryValue> {
+        Conditional.Coalesce([lhs.queryFragment, rhs.queryFragment])
     }
 }