Using SpacetimeDB `1.12.0` on Unity `6000.3.2.f1` reports many "does not exist in the namespace 'SpacetimeDB'"

[rekhoff]

Community Discord members ezoray and mixin have reported errors when using SpacetimeDB version 1.12.0 on Unity 6000.3.2.f1

Doing so results in hundreds of errors in the Unity logs about missing data types within SpacetimeDB.

Steps to Reproduce

1. Start a new Unity project on Unity version 6000.3.2.f1
2. Open package manager and import Unity using Import package from git URL... , entering the URL of:
   https://github.com/clockworklabs/com.clockworklabs.spacetimedbsdk.git
3. Observe errors in Unity's Console window