rsz: collapse buffer-size comparator to a make_tuple compare

Per review, express the (cap, id) lexicographic order as a single
std::make_tuple comparison. Each key is still evaluated once per cell, and
the explicit if-chain goes away.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Signed-off-by: Øyvind Harboe <oyvind.harboe@zylin.com>

Author: oharboe

src/rsz/src/Rebuffer.cc

@@ -1500,12 +1500,8 @@ void Rebuffer::init()
   }
 
   std::ranges::sort(buffer_sizes_, [=](BufferSize a, BufferSize b) {
-    const float cin_a = bufferCin(a.cell);
-    const float cin_b = bufferCin(b.cell);
-    if (cin_a != cin_b) {
-      return cin_a < cin_b;
-    }
-    return a.cell->id() < b.cell->id();
+    return std::make_tuple(bufferCin(a.cell), a.cell->id())
+           < std::make_tuple(bufferCin(b.cell), b.cell->id());
   });
 
   buffer_sizes_index_.clear();

src/rsz/src/RepairDesign.cc

@@ -14,6 +14,7 @@
 #include <optional>
 #include <set>
 #include <string>
+#include <tuple>
 #include <utility>
 #include <vector>
 
@@ -647,12 +648,8 @@ void RepairDesign::findBufferSizes()
                    resizer_->buffer_fast_sizes_.end()};
   std::ranges::sort(buffer_sizes_,
                     [=](sta::LibertyCell* a, sta::LibertyCell* b) {
-                      const float cin_a = bufferCin(a);
-                      const float cin_b = bufferCin(b);
-                      if (cin_a != cin_b) {
-                        return cin_a < cin_b;
-                      }
-                      return a->id() < b->id();
+                      return std::make_tuple(bufferCin(a), a->id())
+                             < std::make_tuple(bufferCin(b), b->id());
                     });
 }