address review: replace DIFFICULTY with PREVRANDAO, explain view annotation on system contracts

Author: Troublor

docs/dev/execution/system-contracts.md

@@ -133,6 +133,9 @@ Attempts to access volatile data while disabled revert immediately, preventing b
 
 **Interface:**
 
+Functions are declared `view` so they can be called from `view` contexts.
+The node intercepts these calls and tracks the restriction outside EVM storage, so no state modification occurs.
+
 ```solidity
 interface IMegaAccessControl {
     function disableVolatileDataAccess() external view;

docs/dev/execution/volatile-data.md

@@ -25,10 +25,9 @@ Accessing any of these opcodes triggers a **20,000,000 compute gas** detention c
 | `NUMBER`      | Current block number      |
 | `TIMESTAMP`   | Current block timestamp   |
 | `COINBASE`    | Block beneficiary address |
-| `DIFFICULTY`  | Block difficulty          |
+| `PREVRANDAO`  | Previous block randomness |
 | `GASLIMIT`    | Block gas limit           |
 | `BASEFEE`     | Base fee per gas          |
-| `PREVRANDAO`  | Previous block randomness |
 | `BLOCKHASH`   | Historical block hash     |
 | `BLOBBASEFEE` | Blob base fee             |
 | `BLOBHASH`    | Blob hash lookup          |