GeezerVison

`@vectorcall` with `**kwargs` always delegated to the keyword helper,
which only reads a kwargs dict, so it couldn't be generated.  The
vectorcall now parses positionals with the shared positional emitter and
builds the dict from kwnames only when there are keywords, otherwise
passing NULL, as the tuple parser does.

The `*args` and `**kwargs` parsers take the calling convention explicitly
rather than reading `self.fastcall`, which describes the Python-visible
entry point having stack style args, not the vectorcall.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

…ree.Element

xml.etree.ElementTree.Element gains a generated vectorcall.  Keys that
are not strings in `**extra` now raise TypeError on a normal call, as
the Python implementation already did, because vectorcall keywords must
be strings; an explicit `__init__` call and subclasses still accept them.

`@text_signature` keeps the documented `(tag, /, attrib={}, **extra)`:
`attrib` can still be passed by keyword, which the impl pops from `extra`.

Merging the keywords into the attributes now copies them with
PyDict_Copy() instead of PyDict_New() plus PyDict_Update(), and pops
`attrib` with `_Py_ID(attrib)` rather than creating a string per call;
SubElement shares that helper.

pyperf microbenchmark (PGO+LTO, run serially):

| Benchmark              | base    | Element               |
|------------------------|:-------:|:---------------------:|
| E('a', x='1')          | 116 ns  | 76.3 ns: 1.52x faster |
| E('a')                 | 42.6 ns | 28.2 ns: 1.51x faster |
| E('a', attrib=d)       | 122 ns  | 82.8 ns: 1.47x faster |
| E('a', d)              | 73.8 ns | 53.6 ns: 1.38x faster |
| SE(E('p'), 'a', x='1') | 161 ns  | 120 ns: 1.35x faster  |
| E('a', d, y='2')       | 102 ns  | 80.3 ns: 1.27x faster |
| S('a')                 | 49.4 ns | 39.8 ns: 1.24x faster |

Benchmark code:

```python
import pyperf

runner = pyperf.Runner()
setup = ("from _elementtree import Element as E, SubElement as SE\n"
         "d = {'x': '1'}\n"
         "class S(E): pass")
for stmt in ["E('a')", "E('a', d)", "E('a', x='1')", "E('a', d, y='2')",
             "E('a', attrib=d)", "S('a')", "SE(E('p'), 'a', x='1')"]:
    runner.timeit(stmt, stmt, setup)
```

Co-Authored-By: Claude Opus 5.5 <[email protected]>

…eywords

Co-Authored-By: Claude Opus 5.5 <[email protected]>

`*args as name` already set the C name; `**kwargs as name` failed to
parse because the 'as' regex only allowed a single leading star.

Co-Authored-By: Claude Opus 5.5 <[email protected]>