Fix rewrite-csharp integTest: stop dotnet run build output corrupting the RPC stream

[knutwannheden]

Motivation

main CI has been red since 2026-06-12, with every run failing identically at
:rewrite-csharp:integTest:

io.moderne.jsonrpc.JsonRpcException: {code=-32603, message='Internal error: JSON-RPC peer closed the stream'}

The failures appeared on commits entirely unrelated to C# (e.g. a
ChangeMethodInvocationReturnType fix, a Python type-attribution change),
which is the tell that the trigger was external rather than a code regression.

The integTest launches the C# server with dotnet run --project ... --framework net10.0.
dotnet run performs an implicit restore + build and writes MSBuild/NuGet
output to stdout — the same stream used for the JSON-RPC bridge. A NuGet
security advisory (NU1903 / GHSA-hv8m-jj95-wg3x) was published around
2026-06-12 for MessagePack 2.5.187 (pulled transitively). NuGet's restore
audit then started printing a warning to stdout, corrupting the RPC framing and
killing the peer. Reproduced locally, the warning is visible inline in the stream:

Invalid Request: Expected Content-Length header but received
'...OpenRewrite.csproj : warning NU1903: Package 'MessagePack' 2.5.187 has a
known high severity vulnerability, https://github.com/advisories/GHSA-hv8m-jj95-wg3x ...'

Production launches a pre-built apphost (buildToolPathCommand), so only the
test launcher (buildCsprojCommand) was affected.

Summary

• Add --no-build to the dotnet run command in
  CSharpRewriteRpc.buildCsprojCommand. --no-build implies --no-restore,
  so no restore audit runs and no MSBuild/NuGet output can reach stdout.
• This is safe because the project is always pre-built by the csharpBuild
  Gradle task that this command's only caller (integTest) depends on. It also
  matches the --no-build already used by the csharpTest task in the same
  build file.
• --verbosity quiet was rejected: it does not suppress the NU1903 warning
  on stdout; only skipping restore/build does.

Test plan

• ./gradlew :rewrite-csharp:integTest — 17 tests, 0 failures (was 16/17
  failing before the fix).
• Confirmed via direct dotnet run invocation that --no-build yields a
  clean stdout (no NU1903), while --verbosity quiet still leaks it.