Add RzIterator support to the bindgen and linter

[notxvilka]

Bindgen:

• Bind RzIterator as a class. rz_iterator_next is exposed as next()
  and rz_iterator_free as the destructor. Since RzIterator is
  type-erased in C (rz_iterator_next returns a borrowed void *),
  elements are yielded as opaque pointers. A new RzIteratorIterator
  python helper implements the iterator protocol on top of next(), so
  every RzIterator * return value works directly in a for loop. On
  exhaustion it hands ownership to SWIG via thisown so the idiomatic
  for x in coll.as_iter(): ... frees the iterator deterministically.
• Add as_iter / as_iter_keys / as_iter_mut to every hashtable type
  (HtPP, HtPU, HtUP, HtUU, HtSP, HtSS, HtSU). RzSetS / RzSetU are typedef
  aliases of HtSP / HtUP, so this covers sets transitively.
• Support add_python_method on Class (it previously only existed on
  Generic), used for RzIterator.__iter__.

Linter:

• Recognize and validate RzIterator type comments. The element type is
  often not known statically, so RzIterator is kept out of generic_types
  (the comment stays optional); when present it must name exactly one type,
  unlike the two-parameter RzGraph / HtPP form.
• Normalize surrounding whitespace in type comments so the space-padded
  /* <T> */ style used by the RzIterator helpers is accepted alongside
  the existing compact /*<T>*/ style. Existing annotations have no
  padding, so this is a no-op for them.

Closes #67