Fix possible double score submission when auto-retrying via perfect mod

Closes https://github.com/ppy/osu/issues/26035.

`submitOnFailOrQuit()`, as the name suggests, can be called both when
the player has failed, or when the player screen is being exited from.
Notably, when perfect mod with auto-retry is active, the two happen
almost simultaneously.

This double call exposes a data race in `submitScore()` concerning the
handling of `scoreSubmissionSource`. The race could be experimentally
confirmed by applying the following patch:

diff --git a/osu.Game/Screens/Play/SubmittingPlayer.cs b/osu.Game/Screens/Play/SubmittingPlayer.cs
index 83adf1f960..76dd29bbdb 100644
--- a/osu.Game/Screens/Play/SubmittingPlayer.cs
+++ b/osu.Game/Screens/Play/SubmittingPlayer.cs
@@ -228,6 +228,7 @@ private Task submitScore(Score score)
                 return Task.CompletedTask;
             }

+            Logger.Log($"{nameof(scoreSubmissionSource)} is {(scoreSubmissionSource == null ? "null" : "not null")}");
             if (scoreSubmissionSource != null)
                 return scoreSubmissionSource.Task;

@@ -237,6 +238,7 @@ private Task submitScore(Score score)

             Logger.Log($"Beginning score submission (token:{token.Value})...");

+            Logger.Log($"creating new {nameof(scoreSubmissionSource)}");
             scoreSubmissionSource = new TaskCompletionSource<bool>();
             var request = CreateSubmissionRequest(score, token.Value);

which would result in the following log output:

	[runtime] 2024-01-02 09:54:13 [verbose]: scoreSubmissionSource is null
	[runtime] 2024-01-02 09:54:13 [verbose]: scoreSubmissionSource is null
	[runtime] 2024-01-02 09:54:13 [verbose]: Beginning score submission (token:36780)...
	[runtime] 2024-01-02 09:54:13 [verbose]: creating new scoreSubmissionSource
	[runtime] 2024-01-02 09:54:13 [verbose]: Beginning score submission (token:36780)...
	[runtime] 2024-01-02 09:54:13 [verbose]: creating new scoreSubmissionSource
	[network] 2024-01-02 09:54:13 [verbose]: Performing request osu.Game.Online.Solo.SubmitSoloScoreRequest
	[network] 2024-01-02 09:54:14 [verbose]: Request to https://dev.ppy.sh/api/v2/beatmaps/869310/solo/scores/36780 successfully completed!
	[network] 2024-01-02 09:54:14 [verbose]: SubmitSoloScoreRequest finished with response size of 639 bytes
	[network] 2024-01-02 09:54:14 [verbose]: Performing request osu.Game.Online.Solo.SubmitSoloScoreRequest
	[runtime] 2024-01-02 09:54:14 [verbose]: Score submission completed! (token:36780 id:20247)
	[network] 2024-01-02 09:54:14 [verbose]: Request to https://dev.ppy.sh/api/v2/beatmaps/869310/solo/scores/36780 successfully completed!
	[network] 2024-01-02 09:54:14 [verbose]: SubmitSoloScoreRequest finished with response size of 639 bytes
	[runtime] 2024-01-02 09:54:14 [error]: An unhandled error has occurred.
	[runtime] 2024-01-02 09:54:14 [error]: System.InvalidOperationException: An attempt was made to transition a task to a final state when it had already completed.
	[runtime] 2024-01-02 09:54:14 [error]: at osu.Game.Screens.Play.SubmittingPlayer.<>c__DisplayClass30_0.<submitScore>b__0(MultiplayerScore s) in /home/dachb/Documents/opensource/osu/osu.Game/Screens/Play/SubmittingPlayer.cs:line 250

The intention of the submission logic was to only ever create one
`scoreSubmissionSource`, and then reuse this one if a redundant
submission request was made. However, because of the temporal proximity
of fail and quit in this particular case, combined with the fact that
the calls to `submitScore()` are taking place on TPL threads, means that
there is a read-write data race on `scoreSubmissionSource`, wherein the
source can be actually created twice.

This leads to two concurrent score submission requests, which, upon
completion, attempt to transition only _the second_
`scoreSubmissionSource` to a final state (this is because the API
success/failure request callbacks capture `this`, i.e. the entire
`SubmittingPlayer` instance, rather than the `scoreSubmissionSource`
reference specifically).

To fix, ensure correct synchronisation on the read-write critical
section, which should prevent the `scoreSubmissionSource` from being
created multiple times.

osu.Game/Screens/Play/SubmittingPlayer.cs

@@ -41,6 +41,7 @@ namespace osu.Game.Screens.Play
         [Resolved]
         private SessionStatics statics { get; set; }
 
+        private readonly object scoreSubmissionLock = new object();
         private TaskCompletionSource<bool> scoreSubmissionSource;
 
         protected SubmittingPlayer(PlayerConfiguration configuration = null)
@@ -228,16 +229,19 @@ namespace osu.Game.Screens.Play
                 return Task.CompletedTask;
             }
 
-            if (scoreSubmissionSource != null)
-                return scoreSubmissionSource.Task;
+            lock (scoreSubmissionLock)
+            {
+                if (scoreSubmissionSource != null)
+                    return scoreSubmissionSource.Task;
+
+                scoreSubmissionSource = new TaskCompletionSource<bool>();
+            }
 
             // if the user never hit anything, this score should not be counted in any way.
             if (!score.ScoreInfo.Statistics.Any(s => s.Key.IsHit() && s.Value > 0))
                 return Task.CompletedTask;
 
             Logger.Log($"Beginning score submission (token:{token.Value})...");
-
-            scoreSubmissionSource = new TaskCompletionSource<bool>();
             var request = CreateSubmissionRequest(score, token.Value);
 
             request.Success += s =>