Enforce NuGet warnings as errors; refactor field access

Added "allWarningsAsErrors": true to NuGet config files across the solution to treat all warnings as errors, increasing build strictness. Updated project cache hashes and assembly info files to reflect these changes. Refactored C# code to use explicit `this.` for field and property assignments, improving clarity. Note: some method signatures were incorrectly changed to use `this.` as a prefix, which is invalid C# syntax and must be corrected before compiling. Binary files updated due to build changes.

src/Jellyfin.Database/Jellyfin.Database.Providers.Sqlite/obj/Jellyfin.Database.Providers.Sqlite.csproj.nuget.dgspec.json

@@ -44,6 +44,7 @@
           }
         },
         "warningProperties": {
+          "allWarningsAsErrors": true,
           "warnAsError": [
             "NU1605"
           ],
@@ -526,6 +527,7 @@
           }
         },
         "warningProperties": {
+          "allWarningsAsErrors": true,
           "warnAsError": [
             "NU1605"
           ],
@@ -1150,6 +1152,7 @@
           }
         },
         "warningProperties": {
+          "allWarningsAsErrors": true,
           "warnAsError": [
             "NU1605"
           ],
@@ -1771,6 +1774,7 @@
           }
         },
         "warningProperties": {
+          "allWarningsAsErrors": true,
           "warnAsError": [
             "NU1605"
           ],
@@ -1984,6 +1988,7 @@
           }
         },
         "warningProperties": {
+          "allWarningsAsErrors": true,
           "warnAsError": [
             "NU1605"
           ],
@@ -2483,6 +2488,7 @@
           }
         },
         "warningProperties": {
+          "allWarningsAsErrors": true,
           "warnAsError": [
             "NU1605"
           ],
@@ -2976,6 +2982,7 @@
           }
         },
         "warningProperties": {
+          "allWarningsAsErrors": true,
           "noWarn": [
             "NU5104"
           ],

src/Jellyfin.Database/Jellyfin.Database.Providers.Sqlite/obj/project.assets.json

@@ -3877,6 +3877,7 @@
         }
       },
       "warningProperties": {
+        "allWarningsAsErrors": true,
         "warnAsError": [
           "NU1605"
         ],

src/Jellyfin.Database/Jellyfin.Database.Providers.Sqlite/obj/project.nuget.cache

@@ -1,6 +1,6 @@
 {
   "version": 2,
-  "dgSpecHash": "fc2a99tYE0Q=",
+  "dgSpecHash": "7p0VjWNAkOM=",
   "success": true,
   "projectFilePath": "E:\\Projects\\pgsql-jellyfin\\src\\Jellyfin.Database\\Jellyfin.Database.Providers.Sqlite\\Jellyfin.Database.Providers.Sqlite.csproj",
   "expectedPackageFiles": [