fix: address code quality issues in I/Q/T/C regions

- Add disposed checks to MemoryRegion base class Read/Write/Clear
- Add proper Dispose(bool) virtual method to MemoryRegion
- Remove redundant _disposed fields from I/Q regions
- Add timerNumber/counterNumber > 0 validation in T/C regions
- Add XML documentation to T/C region public methods
- Add overflow validation in T/C region constructors

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>