rsz: cache bufferCin() in the buffer-size comparator

Per review, hoist bufferCin() into locals so each comparison does two
port-cap lookups instead of up to four.

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

@@ -1500,8 +1500,10 @@ void Rebuffer::init()
   }
 
   std::ranges::sort(buffer_sizes_, [=](BufferSize a, BufferSize b) {
-    if (bufferCin(a.cell) != bufferCin(b.cell)) {
-      return bufferCin(a.cell) < bufferCin(b.cell);
+    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();
   });

src/rsz/src/RepairDesign.cc

@@ -647,8 +647,10 @@ void RepairDesign::findBufferSizes()
                    resizer_->buffer_fast_sizes_.end()};
   std::ranges::sort(buffer_sizes_,
                     [=](sta::LibertyCell* a, sta::LibertyCell* b) {
-                      if (bufferCin(a) != bufferCin(b)) {
-                        return bufferCin(a) < bufferCin(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();
                     });