all: cleanup the APIs for initializing genesis (#25473)

* all: polish tests

* core: apply feedback from Guillaume

* core: fix comment

consensus/clique/snapshot_test.go

@@ -403,7 +403,7 @@ func TestClique(t *testing.T) {
 		}
 		// Create a pristine blockchain with the genesis injected
 		db := rawdb.NewMemoryDatabase()
-		genesis.Commit(db)
+		genesisBlock := genesis.MustCommit(db)
 
 		// Assemble a chain of headers from the cast votes
 		config := *params.TestChainConfig
@@ -414,7 +414,7 @@ func TestClique(t *testing.T) {
 		engine := New(config.Clique, db)
 		engine.fakeDiff = true
 
-		blocks, _ := core.GenerateChain(&config, genesis.ToBlock(db), engine, db, len(tt.votes), func(j int, gen *core.BlockGen) {
+		blocks, _ := core.GenerateChain(&config, genesisBlock, engine, db, len(tt.votes), func(j int, gen *core.BlockGen) {
 			// Cast the vote contained in this block
 			gen.SetCoinbase(accounts.address(tt.votes[j].voted))
 			if tt.votes[j].auth {