fix(cargo): preserve compiler warnings in cargo test output on passing runs

[CryptoKrad]

Summary

• rtk cargo test silently dropped compile-phase warning: blocks on passing runs — an agent reading cargo test: N passed concluded the build was clean while rustc had emitted warnings. Since exit-0 runs get no tee log, the information was unrecoverable (same class as the never_worse size-only guard: the lie is smaller, so it passes).
• Fix mirrors CargoBuildHandler's warning capture into both paths: CargoTestHandler (streaming) now streams warning blocks live, and filter_cargo_test (buffered/pipe) collects them, capped at CAP_WARNINGS with an +N more marker. The compact summary gains [N compiler warnings]; the aggregate generated N warnings line stays stripped.
• Buffered path hard-terminates a warning block on section markers (failures: / test result: / test / ---- / error) so a short warning block can never swallow a following section.

Test plan

• cargo fmt --all --check && cargo clippy --all-targets && cargo test — fmt clean, clippy 0 issues, 2394 passed / 0 failed (+ integration suites green)
• 2 new regression tests: test_filter_cargo_test_all_pass_preserves_compiler_warnings (buffered) and test_streamed_cargo_test_handler_preserves_compiler_warnings (streaming) — assert warning survival, [N compiler warnings] annotation, and aggregate-line stripping
• Manual testing on a crate with a dead-code warning: passing run now shows the warning block + cargo test: 3 passed (2 suites, 0.00s) [1 compiler warnings] (exit 0); failing run still shows failure detail with exit 101 == raw; rtk cargo build output unchanged (consistency restored between build and test)

🤖 Generated with Claude Code

https://claude.ai/code/session_01K5bb4GKf9CNKP9uYhFDvsz

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