core, eth, internal, rpc: implement final block (#24282)

* eth: core: implement finalized block

* eth/catalyst: fix final block

* eth/catalyst: update finalized head gauge

* internal/jsre/deps: updated web3.js to allow for finalized block

* eth/catalyst: make sure only one thread can call fcu

* eth/catalyst: nitpicks

* eth/catalyst: use plain mutex

* eth: nitpicks

core/blockchain_reader.go

@@ -49,6 +49,12 @@ func (bc *BlockChain) CurrentFastBlock() *types.Block {
 	return bc.currentFastBlock.Load().(*types.Block)
 }
 
+// CurrentFinalizedBlock retrieves the current finalized block of the canonical
+// chain. The block is retrieved from the blockchain's internal cache.
+func (bc *BlockChain) CurrentFinalizedBlock() *types.Block {
+	return bc.currentFinalizedBlock.Load().(*types.Block)
+}
+
 // HasHeader checks if a block header is present in the database or not, caching
 // it if present.
 func (bc *BlockChain) HasHeader(hash common.Hash, number uint64) bool {