[python] Add test cases for flatten-property unknown type and read-only scenarios

[Copilot]

Adds Python mock API tests covering two new Spector scenarios from Azure/typespec-azure#3729 for @flattenProperty edge cases.

Spec dependency bump

• @azure-tools/azure-http-specs: 0.1.0-alpha.38-dev.2 → 0.1.0-alpha.38-dev.4 (adds the two new scenarios)

New test cases (sync + async)

putFlattenUnknownModel — flatten is a no-op on unknown type; properties stays as a top-level field:

def test_put_flatten_unknown_model(client):
    result = client.put_flatten_unknown_model(FlattenUnknownModel(name="foo"))
    assert result.name == "test"
    assert result.properties == {"key1": "value1", "key2": "value2"}

putFlattenReadOnlyModel — model whose flattened sub-object contains only read-only properties; uses the mapping constructor Solution({"name": "foo"}) so the empty properties bag is not serialized into the request body, matching the server's expected {"name": "foo"}. Read-only response fields are asserted via dict access since the generator stores them at the top level of the raw dict:

def test_put_flatten_read_only_model(client):
    result = client.put_flatten_read_only_model(Solution({"name": "foo"}))
    assert result.name == "foo"
    assert result["solutionId"] == "solution1"
    assert result["title"] == "Solution Title"
    assert result["content"] == "Solution Content"

Original prompt

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This section details on the original issue you should resolve

<issue_title>[python] add test case for Azure/typespec-azure#3729</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 Azure/typespec-azure#3729</issue_description>

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

• Fixes [python] add test case for https://github.com/Azure/typespec-azure/pull/3729 #9848

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