Expand integration test coverage: NON_VIRTUAL_NETTY and mockless modes

[Copilot]

Integration tests only exercised VIRTUAL_NETTY with a live mock server, leaving NON_VIRTUAL_NETTY and the mockless code path entirely untested. This is the codified verification that mockless behavior is correct and equivalent across modes.

Changes

• Expanded test matrix — serverConfigurations() now covers four combinations:

  • VIRTUAL_NETTY + mock server (existing)
  • NON_VIRTUAL_NETTY + mock server
  • VIRTUAL_NETTY + mockless
  • NON_VIRTUAL_NETTY + mockless

• startServers accepts mockless flag — the mock server is always started (so mock-server tests work uniformly), but the handoff server skips the HTTP call when mockless=true, exercising doMocklessProcessing directly

• Test display names promoted to arg {3} — description index updated to match the new 4-argument Arguments tuples

• Javadoc updated — notes that NETTY_SCHEDULER is excluded because it requires -Djdk.virtualThreadScheduler.implClass=io.netty.loom.NettyScheduler

All three testable modes (VIRTUAL_NETTY, NON_VIRTUAL_NETTY, mock and mockless) share the same HandoffHandler/doMocklessProcessing code path — the tests confirm functional equivalence across them.

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