Use metrics to count change in entry count

This lets us run gc slower safely

ConflictSet.cpp

@@ -3246,6 +3246,8 @@ struct __attribute__((visibility("hidden"))) ConflictSet::Impl {
     InternalVersionT::zero = tls.zero = oldestVersion;
 
     assert(writeVersion >= newestVersionFullPrecision);
+    assert(tls.accum.entries_erased == 0);
+    assert(tls.accum.entries_inserted == 0);
 
     if (oldestExtantVersion < writeVersion - kMaxCorrectVersionWindow)
         [[unlikely]] {
@@ -3273,15 +3275,20 @@ struct __attribute__((visibility("hidden"))) ConflictSet::Impl {
       auto begin = std::span<const uint8_t>(w.begin.p, w.begin.len);
       auto end = std::span<const uint8_t>(w.end.p, w.end.len);
       if (w.end.len > 0) {
-        keyUpdates += 3;
         addWriteRange(root, begin, end, InternalVersionT(writeVersion), &tls,
                       this);
       } else {
-        keyUpdates += 2;
         addPointWrite(root, begin, InternalVersionT(writeVersion), &tls, this);
       }
     }
 
+    // Run gc at least 150% the rate we're inserting entries
+    keyUpdates +=
+        (std::max<int64_t>(
+             tls.accum.entries_inserted - tls.accum.entries_erased, 0) *
+         3) >>
+        1;
+
     memory_bytes.set(totalBytes);
     point_writes_total.add(tls.accum.point_writes);
     range_writes_total.add(tls.accum.range_writes);