feat: declare the attribute contracts the api mixins rely on

[blaipr]

The api/ counterpart to #50, and the same shape of problem: mixins that read attributes the class they are mixed into supplies, with the contract written down nowhere. 131 type errors on main become 91, without annotating a single function signature.

HasStatus is the clearest case. It reads self.status, self.get, self.related, self.walk, self.result_stdout, self.result_traceback, self.job_explanation, self.execution_environment, self.id and self.type, and declares none of them, because the Page it is mixed into does. Fifteen diagnostics from one undocumented contract. PageList is the same with json, connection, r, next, previous and get.

Each now states what it needs:

class HasStatus:
    # Supplied by the Page this is mixed into: the first three come from the
    # response body through Page.__getattr__, the rest are Page's own methods.
    # Annotations rather than assignments, so nothing is created at runtime and
    # nothing shadows what Page provides.
    status: str
    id: int
    type: str
    ...

Applied to HasStatus and PageList, then to the six mixins under api/mixins/: has_copy, has_create, has_instance_groups, has_notifications, has_survey and has_variables.

One annotation was wrong and the checker said so, which is the point of having one. json: dict on HasVariables and HasCopy produced two new errors, because the code does self.json.variables and self.json.related, and a plain dict has no such attributes. It is not a plain dict: Page.__init__ stores a PseudoNamespace, which serves keys as attributes. Corrected to json: PseudoNamespace, and the two errors went with it.

Verified that this introduces nothing: the full diagnostic list before and after was diffed, and the set after is a strict subset. 40 errors retired, 0 added.

What is deliberately left, and why it is not in this change:

• Attribute 'id' is not defined on None, six of them, where a .get() that can return None is dereferenced immediately. These are real latent AttributeErrors rather than missing declarations, and each needs a decision about what the absent case should do. That is a bug-fixing change, not a typing one.
• Cannot resolve imported module 'jq' and 'simplejson', both optional imports inside the functions that need them. Installing the extras in the type-check environment resolves both; the code is correct.
• HTTPBasicAuth.__call__ expects a PreparedRequest in pages/base.py, where a namedtuple with a headers attribute is passed instead. That works because the callable only touches headers, but it is a genuine abuse of the interface and wants its own look.

Verified with black --check, flake8, the unit suite at 355 passing, import ascenderkit, and ascender --help.

[ciq-it-service-account]

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