Stable scores should be using updated grade definitions

[peppy]

As touched on in #26579, both server side and client should be recalculating grades of converted scores, else things are going to get very weird on global leaderboards. Hopefully this is not a contentious issue.

This is going to require a reprocess of all scores server-side, and some client side migration too.

[bdach]

I'll prepare a diff that does this, but one thing I'm not entirely clear on is what such a change is going to mean for users' rank counts. Are we going to recalculate users' rank count totals to use new grades? I imagine some people may not be very happy about that, and I think this'd be a change that would immediately affect users even on the "stable" site instance...

[bdach]

In theory something like the following should work:

https://github.com/ppy/osu/compare/master...bdach:osu:use-new-ranks-everywhere?expand=1
https://github.com/ppy/osu-queue-score-statistics/compare/master...bdach:osu-queue-score-statistics:use-new-ranks-everywhere?expand=1

Initial tests look promising, although I'll need to apply some extra care to make sure the simplifications I applied there are 100% correct. This would be done by running some sheets.

Also holding off from PRing this until we figure out what to do with rank counts as per comment above.

[peppy]

Are we going to recalculate users' rank count totals to use new grades?

I think this will be an afterthought, depends on how people receive the new scoring and everything else. For now it wouldn't change. If/when it changes, it would be a matter of enabling the correct processor on score statistics processor and disabling the rank count increase on web-10, then reprocessing.

[peppy]

When this is applied, please cherry pick the verify step from https://github.com/ppy/osu-queue-score-statistics/compare/master...peppy:osu-queue-score-statistics:verify-score-ranks?expand=1

[peppy]

@bdach i wrote a test which may help with this (in conjunction with #26630)

diff --git a/osu.Game.Tests/Beatmaps/Formats/LegacyScoreDecoderTest.cs b/osu.Game.Tests/Beatmaps/Formats/LegacyScoreDecoderTest.cs
index e56dff74c3..e345a46192 100644
--- a/osu.Game.Tests/Beatmaps/Formats/LegacyScoreDecoderTest.cs
+++ b/osu.Game.Tests/Beatmaps/Formats/LegacyScoreDecoderTest.cs
@@ -252,7 +252,7 @@ public void TestSoloScoreData()
         }
 
         [Test]
-        public void AccuracyAndRankOfStableScorePreserved()
+        public void AccuracyOfStableScorePreserved()
         {
             var memoryStream = new MemoryStream();
 
@@ -292,6 +292,47 @@ public void AccuracyAndRankOfStableScorePreserved()
             });
         }
 
+        [Test]
+        public void RankOfStableScoreUsesLazerDefinitions()
+        {
+            var memoryStream = new MemoryStream();
+
+            // local partial implementation of legacy score encoder
+            // this is done half for readability, half because `LegacyScoreEncoder` forces `LATEST_VERSION`
+            // and we want to emulate a stable score here
+            using (var sw = new SerializationWriter(memoryStream, true))
+            {
+                sw.Write((byte)0); // ruleset id (osu!)
+                sw.Write(20240116); // version (anything below `LegacyScoreEncoder.FIRST_LAZER_VERSION` is stable)
+                sw.Write(string.Empty.ComputeMD5Hash()); // beatmap hash, irrelevant to this test
+                sw.Write("username"); // irrelevant to this test
+                sw.Write(string.Empty.ComputeMD5Hash()); // score hash, irrelevant to this test
+                sw.Write((ushort)195); // count300
+                sw.Write((ushort)1); // count100
+                sw.Write((ushort)4); // count50
+                sw.Write((ushort)0); // countGeki
+                sw.Write((ushort)0); // countKatu
+                sw.Write((ushort)0); // countMiss
+                sw.Write(12345678); // total score, irrelevant to this test
+                sw.Write((ushort)1000); // max combo, irrelevant to this test
+                sw.Write(false); // full combo, irrelevant to this test
+                sw.Write((int)LegacyMods.Hidden); // mods
+                sw.Write(string.Empty); // hp graph, irrelevant
+                sw.Write(DateTime.Now); // date, irrelevant
+                sw.Write(Array.Empty<byte>()); // replay data, irrelevant
+                sw.Write((long)1234); // legacy online ID, irrelevant
+            }
+
+            memoryStream.Seek(0, SeekOrigin.Begin);
+            var decoded = new TestLegacyScoreDecoder().Parse(memoryStream);
+
+            Assert.Multiple(() =>
+            {
+                // In stable this would be an A because there are over 1% 50s. But that's not a thing in lazer.
+                Assert.That(decoded.ScoreInfo.Rank, Is.EqualTo(ScoreRank.S));
+            });
+        }
+
         [Test]
         public void AccuracyOfLazerScorePreserved()
         {