Make the type-name allocator aware of the identifiers the generator emits
itself (`Root` alias, `Skip`/`RootScalar` Kind enumerators) so user `$defs`
names can no longer collide with them. Array-kind names (`Arr0`, `Arr1`, ...)
are now allocated only after checking for object/enum names, preventing
duplicate `Kind` enumerators when a schema defines e.g. `Arr0`.
Add Python regression tests that also syntax-check the generated headers
with a C++ compiler.
Closes#21
weaselbot