[python] Add mock API tests for AlternateInitialVerb POST pagination scenario

[Copilot]

Adds Python SDK mock API tests for the Payload_Pageable_ServerDrivenPagination_AlternateInitialVerb_post scenario from #9966 — pagination where the initial request is a POST (with filter body) and subsequent next-link fetches use GET.

Changes

• package.json: Bump @typespec/http-specs to 0.1.0-alpha.35-dev.4 (first version published after Alternate initial verb #9966 merged that includes the new scenario)
• test_payload_pageable.py / test_payload_pageable_async.py: Add sync + async tests calling the new alternate_initial_verb.post() operation

def test_alternate_initial_verb_post(client: PageableClient):
    result = list(client.server_driven_pagination.alternate_initial_verb.post(Filter(filter="foo eq bar")))
    assert_result(result)  # expects 4 pets: dog, cat, bird, fish across 2 pages

Tests live in generic_mock_api_tests (shared between azure/unbranded flavors) since both generated clients expose the same payload.pageable import path.

Original prompt

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This section details on the original issue you should resolve

<issue_title>[python] add test case for #9966
</issue_title>
<issue_description>follow skill https://github.com/microsoft/typespec/blob/main/.github/skills/python-sdk-spector-mock-api-tests/SKILL.md to write test case for #9966
</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes [python] add test case for https://github.com/microsoft/typespec/pull/9966  #10072

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[pkg-pr-new]

Open in StackBlitz

npm i https://pkg.pr.new/@typespec/http-client-python@10075

commit: 69992b4

[github-actions]

All changed packages have been documented.

• ✅ @typespec/http-client-python

Show changes

@typespec/http-client-python - internal ✏️

Add mock API test case for the AlternateInitialVerb POST pagination scenario where the initial request uses POST with a filter body and subsequent next link requests use GET.

[msyyc]

move to #10068