ci(test): mark overload/streaming RPC tests exclusive (#193)

server_test (overload), proto_over_http_protocol_streaming_rpc_test and
std_protocol_streaming_rpc_test stress the whole machine; under concurrent CI
load they crash (SIGSEGV/SIGABRT) or time out nondeterministically though they
pass in isolation. Mark them exclusive so blade runs them alone.

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

flare/rpc/BUILD

@@ -239,7 +239,10 @@ cc_test(
     '//flare/testing:main',
     '//thirdparty/gflags:gflags',
     '//thirdparty/jsoncpp:jsoncpp',
-  ]
+  ],
+  # Has overload tests that stress the whole server; under concurrent CI load
+  # they crash (SIGSEGV) / time out nondeterministically. Run alone.
+  exclusive = True,
 )
 
 cc_test(

flare/rpc/protocol/protobuf/BUILD

@@ -244,7 +244,10 @@ cc_test(
     '//flare/testing:echo_service_proto_flare',
     '//flare/testing:endpoint',
     '//flare/rpc:rpc',
-  ]
+  ],
+  # Streaming RPC stress: resource-heavy, flakes (SIGABRT/timeout) under
+  # concurrent CI load. Run alone.
+  exclusive = True,
 )
 
 cc_library(
@@ -297,6 +300,9 @@ cc_test(
     '//flare/testing:echo_service_proto_flare',
     '//flare/rpc:rpc',
   ],
+  # Streaming RPC stress: resource-heavy, flakes (SIGABRT/timeout) under
+  # concurrent CI load. Run alone.
+  exclusive = True,
 )
 
 cc_library(