As far as I can tell all accesses are safe due to update thread
guarantees. The only weird one may be async writes during a
`BlockAllOperations`, but the `Compact` loop should handle this quite
amicably.
Not really sure how to improve this further, but should help with cases
like this:
```csharp
[runtime] 2022-06-28 05:32:06 [verbose]: 💨 Class: TestSceneSpectatorPlayback
[runtime] 2022-06-28 05:32:06 [verbose]: 🔶 Test: TestWithSendFailure
[runtime] 2022-06-28 05:32:06 [verbose]: 🔸 Step #1 Setup containers
[runtime] 2022-06-28 05:32:06 [verbose]: Received 1 new frames (total 1 of 2)
[runtime] 2022-06-28 05:32:06 [verbose]: 🔸 Step #2 received frames
[runtime] 2022-06-28 05:32:06 [verbose]: Received 6 new frames (total 7 of 8)
[runtime] 2022-06-28 05:32:06 [verbose]: Received 6 new frames (total 13 of 19)
[runtime] 2022-06-28 05:32:06 [verbose]: Received 6 new frames (total 19 of 29)
[runtime] 2022-06-28 05:32:06 [verbose]: Received 6 new frames (total 25 of 44)
[runtime] 2022-06-28 05:32:06 [verbose]: Received 6 new frames (total 31 of 45)
[runtime] 2022-06-28 05:32:06 [verbose]: Received 6 new frames (total 37 of 59)
[runtime] 2022-06-28 05:32:06 [verbose]: Received 6 new frames (total 43 of 67)
[runtime] 2022-06-28 05:32:06 [verbose]: Received 6 new frames (total 49 of 125)
[runtime] 2022-06-28 05:32:06 [verbose]: Received 6 new frames (total 55 of 126)
[runtime] 2022-06-28 05:32:06 [verbose]: Received 6 new frames (total 61 of 127)
[runtime] 2022-06-28 05:32:06 [verbose]: Received 6 new frames (total 67 of 128)
[runtime] 2022-06-28 05:32:06 [verbose]: Received 6 new frames (total 73 of 129)
[runtime] 2022-06-28 05:32:06 [verbose]: Received 6 new frames (total 79 of 130)
[runtime] 2022-06-28 05:32:06 [verbose]: Received 6 new frames (total 85 of 131)
[runtime] 2022-06-28 05:32:06 [verbose]: ✔️ 22 repetitions
[runtime] 2022-06-28 05:32:06 [verbose]: Received 6 new frames (total 91 of 132)
[runtime] 2022-06-28 05:32:06 [verbose]: Received 6 new frames (total 97 of 133)
[runtime] 2022-06-28 05:32:06 [verbose]: Received 6 new frames (total 103 of 134)
[runtime] 2022-06-28 05:32:06 [verbose]: Received 6 new frames (total 109 of 135)
[runtime] 2022-06-28 05:32:06 [verbose]: Received 6 new frames (total 115 of 136)
[runtime] 2022-06-28 05:32:06 [verbose]: Received 6 new frames (total 121 of 137)
[runtime] 2022-06-28 05:32:06 [verbose]: 🔸 Step #3 start failing sends
[runtime] 2022-06-28 05:32:06 [verbose]: Received 6 new frames (total 127 of 138)
[runtime] 2022-06-28 05:32:06 [verbose]: 🔸 Step #4 wait for send attempts
[runtime] 2022-06-28 05:32:06 [verbose]: 🔸 Step #5 frames did not increase
[runtime] 2022-06-28 05:32:06 [verbose]: 💥 Failed
[runtime] 2022-06-28 05:32:06 [verbose]: ⏳ Currently loading components (0)
[runtime] 2022-06-28 05:32:06 [verbose]: 🧵 Task schedulers
[runtime] 2022-06-28 05:32:06 [verbose]: LoadComponentsAsync (standard) concurrency:4 running:0 pending:0
[runtime] 2022-06-28 05:32:06 [verbose]: LoadComponentsAsync (long load) concurrency:4 running:0 pending:0
[runtime] 2022-06-28 05:32:06 [verbose]: 🎱 Thread pool
[runtime] 2022-06-28 05:32:06 [verbose]: worker: min 1 max 32,767 available 32,766
[runtime] 2022-06-28 05:32:06 [verbose]: completion: min 1 max 1,000 available 1,000
[runtime] 2022-06-28 05:32:06 [verbose]: Host execution state changed to Stopping
```
https://teamcity.ppy.sh/buildConfiguration/Osu_Build/811?hideProblemsFromDependencies=false&hideTestsFromDependencies=false&expandBuildTestsSection=true
After a `BlockAllOperations`, the restoration of the `updateRealm`
instance is not instance. It is posted to a `SynchronizationContext`.
The assertion which has been removed in this commit was assuming it
would always be an immediate operation.
To ensure this works as expected, I've tracked the initialised state via
a new `bool`.
```csharp
System.TimeoutException : Attempting to block for migration took too long.
1) Host threw exception System.AggregateException: One or more errors occurred. (: )
---> NUnit.Framework.AssertionException: :
at osu.Framework.Logging.ThrowingTraceListener.Fail(String message1, String message2)
at System.Diagnostics.TraceInternal.Fail(String message, String detailMessage)
at System.Diagnostics.TraceInternal.TraceProvider.Fail(String message, String detailMessage)
at System.Diagnostics.Debug.Fail(String message, String detailMessage)
at osu.Game.Database.RealmAccess.BlockAllOperations() in /opt/buildagent/work/ecd860037212ac52/osu.Game/Database/RealmAccess.cs:line 813
at osu.Game.OsuGameBase.<>c__DisplayClass108_1.<Migrate>b__0() in /opt/buildagent/work/ecd860037212ac52/osu.Game/OsuGameBase.cs:line 449
at osu.Framework.Threading.ScheduledDelegate.RunTaskInternal()
at osu.Framework.Threading.Scheduler.Update()
at osu.Framework.Graphics.Drawable.UpdateSubTree()
at osu.Framework.Graphics.Containers.CompositeDrawable.UpdateSubTree()
```
https://teamcity.ppy.sh/buildConfiguration/Osu_Build/322?hideProblemsFromDependencies=false&hideTestsFromDependencies=false&expandBuildTestsSection=true
