Allocation operators on an interface are silently dropped

`operator new`, `operator delete` and their array forms are implicitly static, so `protocol_interface_function_infos` drops them at `if (is_static_member(member)) continue;` with no diagnostic:

```cpp
struct I { int f() const; void* operator new(std::size_t); void operator delete(void*) noexcept; };
// conforms against any C with int f() const; the allocation functions vanish
```

Meanwhile #388 adds `NamesAllocationOperatorsWithNoQualifiersAsTheyAreStatic` to name_mangling_tests.cc and `nw`/`dl`/`na`/`da` cases to `base_name_of`, none of which is reachable through the library. `operator co_await`, by contrast, gets a clear "is not supported in a protocol interface" throw.

CONTRIBUTING.md's "Static member functions declared on the interface itself are ignored" arguably covers this. If it is intended, the docs should name the allocation operators explicitly and the mangling cases can go; if not, they should be rejected like `co_await`.

Start with protocol_interface_function_infos and the is_static_member(member) check, then compare the existing operator co_await handling. Review CONTRIBUTING.md, name_mangling_tests.cc, and the base_name_of cases from #388. Done means deciding whether allocation operators are intentionally ignored and documenting them explicitly, or rejecting them with a diagnostic and aligning the mangling tests.

Written by the indexing model from the issue text.