Add blockhash to docs (#5653)

Co-authored-by: ernestognw <ernestognw@gmail.com>

contracts/utils/Blockhash.sol

@@ -14,6 +14,7 @@ pragma solidity ^0.8.20;
  * Before that, only block hashes since the fork block will be available.
  */
 library Blockhash {
+    /// @dev Address of the EIP-2935 history storage contract.
     address internal constant HISTORY_STORAGE_ADDRESS = 0x0000F90827F1C53a10cb7A02335B175320002935;
 
     /**

contracts/utils/README.adoc

@@ -45,6 +45,7 @@ Miscellaneous contracts and libraries containing utility functions you can use t
  * {Panic}: A library to revert with https://docs.soliditylang.org/en/v0.8.20/control-structures.html#panic-via-assert-and-error-via-require[Solidity panic codes].
  * {Comparators}: A library that contains comparator functions to use with the {Heap} library.
  * {CAIP2}, {CAIP10}: Libraries for formatting and parsing CAIP-2 and CAIP-10 identifiers.
+ * {Blockhash}: A library for accessing historical block hashes beyond the standard 256 block limit utilizing EIP-2935's historical blockhash functionality.
 
 [NOTE]
 ====
@@ -156,3 +157,5 @@ Ethereum contracts have no native concept of an interface, so applications must
 {{CAIP2}}
 
 {{CAIP10}}
+
+{{Blockhash}}

docs/modules/ROOT/pages/utilities.adoc

@@ -386,3 +386,22 @@ await instance.multicall([
     instance.interface.encodeFunctionData("bar")
 ]);
 ----
+
+=== Historical Block Hashes
+
+xref:api:utils.adoc#Blockhash[`Blockhash`] provides L2 protocol developers with extended access to historical block hashes beyond Ethereum's native 256-block limit. By leveraging https://eips.ethereum.org/EIPS/eip-2935[EIP-2935]'s history storage contract, the library enables access to block hashes up to 8,191 blocks in the past, making it invaluable for L2 fraud proofs and state verification systems.
+
+The library seamlessly combines native `BLOCKHASH` opcode access for recent blocks (≤256) with EIP-2935 history storage queries for older blocks (257-8,191). It handles edge cases gracefully by returning zero for future blocks or those beyond the history window, matching the EVM's behavior. The implementation uses gas-efficient assembly for static calls to the history storage contract.
+
+[source,solidity]
+----
+contract L1Inbox {
+    using Blockhash for uint256;
+
+    function verifyBlockHash(uint256 blockNumber, bytes32 expectedHash) public view returns (bool) {
+        return blockNumber.blockHash() == expectedHash;
+    }
+}
+----
+
+IMPORTANT: After EIP-2935 activation, it takes 8,191 blocks to completely fill the history storage. Before that, only block hashes since the fork block will be available.