Receiver binding misses non-bare staticmethod spellings (@builtins.staticmethod) #135

Problem

build_scope decides whether a callable has a receiver by exact string membership against
unparsed decorator text (codeanalyzer/dataflow/access_paths.py:255-257):

decorators = {ast.unparse(d) for d in func.decorator_list}
if params[0] in ("self", "cls") and "staticmethod" not in decorators:
    scope.self_name = params[0]

Only the bare spelling staticmethod is recognised. Any other spelling of the same builtin —
@builtins.staticmethod, or from builtins import staticmethod as sm — fails the membership
test, so a static method gets a receiver it does not have, and scope.self_name is later added
as a definition (access_paths.py:472-473), producing a spurious def in the L3/L4 dataflow.

Verified on a0b94ff:

dotted   decorators=['builtins.staticmethod']   self_name='self'   <- wrong
plain    decorators=['staticmethod']            self_name=None
normal   decorators=['staticmethod']            self_name=None

Scope boundary

The receiver-binding predicate only. Does not restructure the decorator schema (#128), and does
not touch classmethod or property handling.

Goals

• Recognise staticmethod by resolved identity, not by unparsed spelling
• Cover the dotted form and an aliased import
• Test asserting self_name is None for each spelling

Caveats and known risks

• Triggers only when the first parameter is named self or cls; a staticmethod with a normal
  first parameter name is unaffected.
• Legal but unusual code, so the blast radius is small and no bug report prompted this.
• A resolved check needs the decorator's qualified_name, which Jedi already computes and stores
  in accessed_symbols; Structured decorator representation: PyDecorator on callable, class, attribute, parameter #128 would make it directly available on the decorator.
• Unverified: whether any current test would have caught the fix regressing.

Definition of done

• @builtins.staticmethod def f(self, x) yields self_name is None
• An aliased-import spelling yields self_name is None
• Bare @staticmethod and undecorated methods keep their current behaviour
• Existing dataflow tests pass unchanged