[python] add test case to improve test coverage

[msyyc]

• [Specs] add case for constant query  #8836
• Add test cases for @clientDefaultValue decorator Azure/typespec-azure#3635
• [http specs] Add new test case for multipart #9139
• [http-specs] Fix bulletPointsModel API signature to match runtime behavior #9200
• [spector] Add test case for special words about model property name #9019
• Add test case for model property named "list" #9259