Desugaring: avoid patdef optimization for lazy vals (#26770)

Fixes #26769

My bad.

## Have you relied on LLM-based tools in this contribution?

No

## How was the solution tested?

New automated tests (including the issue's reproducer, if applicable)

Author: SolalPirelli

compiler/src/dotty/tools/dotc/ast/Desugar.scala

@@ -1616,11 +1616,12 @@ object desugar {
           case _ =>
             // ... except we have one more optimization up our sleeve:
             // if we're in the "simple tuple" case and the RHS is also a tuple, for `val (a, b) = (1, 2)` we can emit `val a = 1; val b = 2`.
-            // We don't do this if there are any types or wildcards involved, since those can require conversions or handling side-effects.
+            // We don't do this if there is laziness or any types or wildcards involved; the latter can require conversions or handling side effects.
             val (firstDef, splitRhs) = rhs match
               case TuplePattern(elems, TypeTree()) if opt == Optimization.SimpleTuple
                                                    && elems.size == variables.size
                                                    && !pat.isInstanceOf[Typed]
+                                                   && !mods.is(Lazy)
                                                    && variables.forall((n, _) => n.name != nme.WILDCARD) =>
                 (Nil, elems)
               case _ =>

tests/run/lazy-val-pattern-2.check

@@ -0,0 +1,7 @@
+a
+c
+b
+1
+2
+1
+2

tests/run/lazy-val-pattern-2.scala

@@ -0,0 +1,8 @@
+object Test:
+  lazy val (a, _, b) = ({println("a"); 1}, {println("c"); 3}, {println("b"); 2})
+  
+  def main(args: Array[String]): Unit =
+    println(a)
+    println(b)
+    println(a)
+    println(b)

tests/run/lazy-val-pattern-3.check

@@ -0,0 +1,5 @@
+a
+1
+2
+1
+2

tests/run/lazy-val-pattern-3.scala

@@ -0,0 +1,8 @@
+object Test:
+  lazy val (a, b) = {println("a"); (1, 2)}
+  
+  def main(args: Array[String]): Unit =
+    println(a)
+    println(b)
+    println(a)
+    println(b)

tests/run/lazy-val-pattern.check

@@ -0,0 +1,6 @@
+a
+b
+1
+2
+1
+2

tests/run/lazy-val-pattern.scala

@@ -0,0 +1,8 @@
+object Test:
+  lazy val (a, b) = ({println("a"); 1}, {println("b"); 2})
+  
+  def main(args: Array[String]): Unit =
+    println(a)
+    println(b)
+    println(a)
+    println(b)