feat: regenerate client from corrected OpenAPI spec

[mekilis]

Summary

• Regenerates the Python client from the corrected Convoy OpenAPI spec produced by fix(docs): OpenAPI spec fidelity for generated SDK clients convoy#2742 (nullable object/map handling, bearer auth security scheme, JSON-only onboard, portal link endpoints_metadata nullability).
• Nullable object/map schemas now generate as *_type_0 union models, replacing the previous non-nullable model classes.

Test plan

• Local suite: 29/29 passing
• Wide smoke against the QA harness passed

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Note

High Risk
Wide generated-surface changes plus bulk onboard wire format and enum renames are breaking for SDK consumers; auth-related AuthRoleType renames can break role checks at runtime.

Overview
Regenerates the Convoy Python client from an updated OpenAPI spec so generated types and HTTP calls match the API more closely.

Bulk onboard no longer accepts a raw File with application/octet-stream. The onboard helpers now take an optional ModelsBulkOnboardRequest and POST JSON (body.to_dict(), Content-Type: application/json).

Nullable object/map fields are modeled as separate *_type_0 types (e.g. event data, custom headers, JSON schemas, filter bulk-update maps). Public exports in models/__init__.py were updated to those names, so imports of the old symbol names will break.

API error envelopes across many *Response400/401/404 models now type data as HandlersStubType0 | None | Unset, with to_dict/from_dict that preserve JSON null and fall back when data is not a stub object.

Enums were reshaped by the generator: AuthRoleType members drop the ROLE_ prefix (e.g. API instead of ROLE_API), and some config header enums add alternate members such as VALUE_1 for empty-string variants.

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