Candidate State Manager and Candidate State Reader

1. CandidateStateManager extends CandidateStateReader
2. Clean up the two interfaces
3. Use appropriate one, e.g., use StateReader in the readonly functions
### Description of the code refactor

### Why is this needed
- [] better/less memory usage
- [] reduce running time
- [] clean (easy-to-understand) data structure or algorithm
- [] remove dead code
- [] better code design or structure (like reduce complexity)
- [] reduce/decouple dependencies between code modules
- [] increase test coverage
- [] better code readability

Start by locating the CandidateStateManager and CandidateStateReader definitions and their usages, especially the readonly functions. Determine how the two interfaces should be cleaned up and which functions should use StateReader; the work is done when the intended interface separation is implemented and relevant tests pass.

Written by the indexing model from the issue text.