fix(cargo): preserve quiet check success output

[YOMXXX]

Summary

• Preserve empty cargo build/check output instead of synthesizing cargo build (0 crates compiled)
• Add streaming and buffered regression tests for quiet successful cargo output

Fixes #2545

Verification

• cargo +1.93.0 test quiet_success_preserves_empty_output -- --nocapture
• cargo +1.93.0 test cargo_build -- --nocapture
• cargo +1.93.0 fmt --all -- --check
• cargo +1.93.0 clippy --all-targets
• cargo +1.93.0 test --all -- --skip small_grep_not_worse_than_plain
• git diff --check
• cargo +1.93.0 run --quiet -- cargo check -q (status=0, bytes=0)

Note: small_grep_not_worse_than_plain is a known upstream baseline failure on develop, so the broad test run skips only that test.