[scudo] Use anonymous namespace for test helper code (#157207)

Tests can be at top-level or inside an anonymous namespace,
doesn't matter.  But putting their helper code inside anonymous
namespaces both makes the code compatible with compiling using
-Wmissing-declarations and might let the compiler optimize the
test good a bit better.

GitOrigin-RevId: 8ddd8045ac3e74ef3273e50973534b35c0620d52
1 file changed