[CPU] Add ASCII diagram for MemoryInput/MemoryOutput memory mapping and reuse (#35340)
### Details:
This PR replaces a todo comment with an inline ASCII diagram
documenting:
- The VariableStateDoubleBuffer double-buffer scheme and how commit()
toggles buffer_num
- The ProxyMemoryBlock zero-copy vs. copy decision for both MemoryInput
and MemoryOutput in-place edges
- The sharedMemFrom() edge used by ReadValueWithSubgraph to achieve
zero-copy through the init subgraph
### AI Assistance:
- *AI assistance used: no / yes* yes
- *If yes, summarize how AI was used and what human validation was
performed (build/tests/manual checks).* used for code review and
corrections