fix: remove unused SQLite native asset warning in TodoApp.BlazorWasm.Client

[adrianhall]

Summary

samples/todoapp-blazor-wasm/TodoApp.BlazorWasm.Client produced a benign, code-less MSBuild warning during a plain dotnet build:

WorkloadManifest.targets(124,5): warning : @(NativeFileReference) is not empty, but the native references
won't be linked in, because neither $(WasmBuildNative), nor $(RunAOTCompilation) are 'true'.
NativeFileReference=.../sourcegear.sqlite3/3.50.4.5/buildTransitive/net9.0/../../runtimes/browser-wasm/nativeassets/net9.0/e_sqlite3.a

Root cause

CommunityToolkit.Datasync.Client depends unconditionally on Microsoft.EntityFrameworkCore.Sqlite (confirmed by inspecting src/CommunityToolkit.Datasync.Client/CommunityToolkit.Datasync.Client.csproj), which transitively resolves to SourceGear.sqlite3 via SQLitePCLRaw.bundle_e_sqlite3 (the version pinned in this project only to resolve NU1903 - see #492). SourceGear.sqlite3's own buildTransitive/net9.0/SourceGear.sqlite3.targets unconditionally adds a NativeFileReference for e_sqlite3.a whenever $(RuntimeIdentifier) == 'browser-wasm' - independent of which SQLitePCLRaw.bundle_e_sqlite3 version resolves, so pinning a narrower package wouldn't avoid it.

TodoApp.BlazorWasm.Client never uses SQLite/OfflineDbContext (verified: no references to DbContext, Sqlite, or OfflineTable anywhere in the project) - it only uses CommunityToolkit.Datasync.Client for online HTTP access - so this native asset is genuinely unused. The warning itself comes from the .NET SDK's own _CheckBrowserWorkloadNeededButNotAvailable target in WorkloadManifest.targets, which has no diagnostic code and therefore can't be suppressed via NoWarn.

Fix

Remove the specific unused e_sqlite3.a NativeFileReference item from TodoApp.BlazorWasm.Client.csproj before the SDK's browser-workload check target runs:

<Target Name="RemoveUnusedSqliteNativeFileReference" BeforeTargets="_CheckBrowserWorkloadNeededButNotAvailable">
  <ItemGroup>
    <NativeFileReference Remove="@(NativeFileReference)" Condition="'%(Filename)%(Extension)' == 'e_sqlite3.a'" />
  </ItemGroup>
</Target>

This fixes the root cause (an asset that's provably never used) rather than just suppressing the symptom, and is scoped to this single sample project - no change to CommunityToolkit.Datasync.Client or any other sample.

Testing

• dotnet restore + dotnet build samples/todoapp-blazor-wasm/TodoApp.BlazorWasm.sln --configuration Debug (matches build-samples-todoapp-blazor-wasm.yml exactly): negative control confirmed the warning appears twice on a clean build without this change, and zero times with it - 0 Warning(s), 0 Error(s).
• dotnet restore + dotnet build Datasync.Toolkit.sln: clean, 0 Warning(s), 0 Error(s).
• dotnet test tests/CommunityToolkit.Datasync.Client.Test: 1432/1432 passed (unaffected by this samples-only change, confirms no regression).
• Triggered the Build Samples GitHub Actions workflow on this branch in my fork: all 18 jobs succeeded, including todoapp-blazor-wasm / build and the All samples built aggregation job - https://github.com/adrianhall/CommunityToolkit-Datasync/actions/runs/29146333208

Fixes #523