Bug: serialize Python request models with Swagger JSON property names

[daviburg]

Problem

The Python SDK correctly uses snake_case for its public model attributes, but ConnectorHttpClient.send_async serializes dataclass bodies with dataclasses.asdict. That emits Python attribute names rather than the JSON property names declared by the connector Swagger schema.

For a Swagger property such as printBackground, a generated Python model exposes print_background; asdict sends print_background. The generated .NET model sends printBackground through JsonPropertyName. The connector service contract is the Swagger JSON name; language-specific public naming must not change the payload wire format.

Evidence

• Python SDK PR Add new connectors (Phase 3) #54 adds many generated request models with snake_case attributes.
• The shared Python HTTP client uses asdict(body) before json.dumps.
• In the PR Add new connectors (Phase 3) #54 validation snapshot, representative PDF.co fields serialize as paper_size / print_background instead of Swagger paperSize / printBackground.
• The cross-language validation found 266 request-model serialization-key mismatches across the 12 PR Add new connectors (Phase 3) #54 connectors.

This is a pre-existing shared runtime defect, not behavior introduced by the binary-body changes in PR #54.

Expected Fix

1. Preserve idiomatic Python snake_case public attributes and methods.
2. Generate or retain each Swagger JSON property name as explicit serialization metadata.
3. Replace bare asdict request serialization with a shared recursive wire serializer that emits the Swagger property names for dataclasses, nested models, lists, maps, and additional_properties.
4. Continue omitting None values and preserve raw bytes handling without JSON encoding.

Regression Coverage

Add focused tests at the shared runtime boundary that capture the body sent to the transport and assert exact JSON keys for:

• a snake_case property whose Swagger wire name is camelCase;
• nested dataclasses and lists of dataclasses;
• additional_properties / dynamic objects;
• omitted None values; and
• raw binary request bodies.

Add a generated-client contract test using a real PR #54 model, such as PDF.co HtmlToPdfInput, to verify print_background emits printBackground and paper_size emits paperSize.

[hallvictoria]

Expected fix point	Verification
Replace bare asdict with a shared recursive wire serializer	sdk/serialization.py to_wire() exists; http_client.send_async uses json.dumps(to_wire(...)); 0 asdict( usages remain
Swagger JSON name retained as serialization metadata	1254 wire_name mappings emitted across the 12 connectors
The exact PDF.co example	HtmlToPdfInput emits paper_size → paperSize and print_background → printBackground
Omit None, preserve raw bytes, merge additional_properties	Implemented in _dataclass_to_wire / to_wire
snake_case public attributes preserved	Fields stay snake_case, wire name lives only in metadata
Regression coverage	test_sdk_serialization.py + boundary tests in test_sdk_http_client.py