Implement software simulated attnuator library

[wptestyyh]

Type

• Bug fix
• Feature addition
• Feature update
• Documentation
• Build Infrastructure

Side Effects

• Breaking change
• Non-functional change

Goals

• Allow test attenuator gRPC API without hardware

Technical Details

• Add RfAttenuatorFactory interface so the library consumer can call it to create IRfAttenuatorController instance.
• Add IRfAttenuatorController interface so the library consumer can call it to manage attenuator
• Add RfAttenuatorSoftwareSimulated so the test code can test gRPC API without hardware
• Add some utility classes

Test Results

• Tests will be added and run later seperatly in next PR

Reviewer Focus

• None

Future Work

• Attenuator gRPC APIs
• Attenuator gRPC APIs tests

Checklist

• Build target all compiles cleanly.
• clang-format and clang-tidy deltas produced no new output.
• Newly added functions include doxygen-style comment block.