Drop mockito-scala-scalatest test dependency

[ddworak]

Summary

• Removes the mockito-scala-scalatest dependency (and its transitive Mockito/ByteBuddy chain) from restJvmDeps.
• Deletes RestServletTest, the single file that used it. Its 13 scenarios were already covered end-to-end by JettyRestCallTest, SttpRestCallTest, and EndpointsIntegrationTest, which exercise the real RestServlet behind a real Jetty server — strictly higher fidelity than the mock-based variant.
• Ports the one scenario that wasn't already covered against a real servlet (mid-stream failure → server closes the response) into StreamingRestApiTestScenarios via the pre-existing errorStream fixture. Uses an explicit .timeout(5.seconds) so a servlet regression that fails to close the stream fails loudly rather than hanging.

QA impact

• 12/13 former scenarios: now exercised through real HTTP + real Jetty + real RestServlet via JettyRestCallTest — higher coverage than before.
• Mid-stream-error scenario: reimplemented as an integration test, named "mid-stream server error propagates to client" in StreamingRestApiTestScenarios.

Test plan

• sbt rest/test — 128 tests pass across 11 suites.
• sbt rest-jetty/test — 28 tests including the new case pass.
• sbt compile Test/compile — clean across all modules.
• Repo-wide grep for mockito/org.mockito — zero hits.

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