Add comprehensive tests for relay quota management and adversarial scenarios

- Introduced `relay_quota_boundary_blackhat_tests.rs` to validate behavior under quota limits, including edge cases and adversarial conditions.
- Added `relay_quota_model_adversarial_tests.rs` to ensure quota management maintains integrity during bidirectional communication and various load scenarios.
- Created `relay_quota_overflow_regression_tests.rs` to address overflow issues and ensure that quota limits are respected during aggressive data transmission.
- Implemented `route_mode_coherence_adversarial_tests.rs` to verify the consistency of route mode transitions and timestamp management across different relay modes.

src/proxy/client.rs

@@ -1273,3 +1273,7 @@ mod masking_shape_hardening_redteam_expected_fail_tests;
 #[cfg(test)]
 #[path = "tests/client_masking_shape_classifier_fuzz_redteam_expected_fail_tests.rs"]
 mod masking_shape_classifier_fuzz_redteam_expected_fail_tests;
+
+#[cfg(test)]
+#[path = "tests/client_masking_probe_evasion_blackhat_tests.rs"]
+mod masking_probe_evasion_blackhat_tests;