This reimplements attrs_strict.type_validator(), using type equality
instead of isinstance.
This makes my checksum validation script (that mostly just instantiates
model objects, computes a checksum, then discard) run twice as fast.
I'm reusing the exception from attrs_strict for compatibility with
existing code that might rely on it. (Though I don't think there's any).
If you're fine with this diff in principle, I'll add tests for this
new type checker.