[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
• Add Spector tests for pageable LROs Azure/typespec-azure#3695
• [spector] Add test case for special words about model property name #9019
• [http-specs] Fix bulletPointsModel API signature to match runtime behavior #9200
• Add test case for model property named "list" #9259
• Add CSV encoding tests for enum and extensible enum arrays #9390
• Add multi-service tests for older API versions and shared models Azure/typespec-azure#3713