fix(split): serialize split_class as a JSON string in multipart form data

[dex0shubham]

Fixes #76

Problem

client.split() (and the async variant) fails with a 422 when following the documented example. The split_class list of dicts was passed straight into the multipart body, which the HTTP layer flattens into split_class[0][name]-style fields — but the API expects a single JSON-string form field, so the server responds with 'split_class': Field required.

Fix

Serialize split_class with json.dumps(list(split_class)) before building the multipart body, in both the sync and async split() methods. This is the fix suggested by @cmaloney111 in the issue, and matches the existing pattern used for options in resources/v2/parse.py. The public method signature is unchanged — callers still pass a list of dicts.

Tests

Added tests/test_split_params.py, which asserts the request body carries split_class as one JSON string (fails on the previous code, where it was a raw list). Full test suite passes locally apart from pre-existing environment-specific failures (Windows chmod semantics, httpx proxy mounts) that also fail on a clean checkout.

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[Copilot]

Pull request overview

Fixes multipart serialization of split_class for split requests.

Changes:

• JSON-serializes split_class in sync and async clients.
• Adds regression tests for request-body serialization.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
src/landingai_ade/_client.py	Updates sync and async split request serialization.
tests/test_split_params.py	Tests JSON-string request bodies.

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Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated no new comments.