[tmpnet] Misc cleanup to support xsvm warp test PR

- update tmpnet.ReadFlagsMap to avoid returning an unnecessary pointer

- add tmpnet.InterfaceToFlagsMap helper to simplify conversion of
subnet configuration to a FlagsMap for nicer serialization

- update tmpnet.NewNodes to initialize tls and signing keys so that
nodes returned by this method can be used to extract the validator IDs
for a subnet

- switch tmpnet.Chain.Genesis back to a byte array. A previous attempt
to improve the readability of tmpnet subnet configuration by
converting to FlagsMap ignored that genesis byte format is VM-specific.

tests/fixture/tmpnet/flags.go

@@ -18,18 +18,34 @@ import (
 type FlagsMap map[string]interface{}
 
 // Utility function simplifying construction of a FlagsMap from a file.
-func ReadFlagsMap(path string, description string) (*FlagsMap, error) {
+func ReadFlagsMap(path string, description string) (FlagsMap, error) {
 	bytes, err := os.ReadFile(path)
 	if err != nil {
 		return nil, fmt.Errorf("failed to read %s: %w", description, err)
 	}
-	flagsMap := &FlagsMap{}
-	if err := json.Unmarshal(bytes, flagsMap); err != nil {
+	flagsMap := FlagsMap{}
+	if err := json.Unmarshal(bytes, &flagsMap); err != nil {
 		return nil, fmt.Errorf("failed to unmarshal %s: %w", description, err)
 	}
 	return flagsMap, nil
 }
 
+// Round-trips the provided interface through JSON to convert to a
+// FlagsMap. This allows for a cleaner serialization of embedded types
+// such as chain configuration.
+func InterfaceToFlagsMap(v interface{}) (FlagsMap, error) {
+	bytes, err := json.Marshal(v)
+	if err != nil {
+		return nil, err
+	}
+	flagsMap := FlagsMap{}
+	err = json.Unmarshal(bytes, &flagsMap)
+	if err != nil {
+		return nil, err
+	}
+	return flagsMap, nil
+}
+
 // SetDefaults ensures the effectiveness of flag overrides by only
 // setting values supplied in the defaults map that are not already
 // explicitly set.

tests/fixture/tmpnet/network_config.go

@@ -140,7 +140,7 @@ func (n *Network) readChainConfigs() error {
 		if err != nil {
 			return err
 		}
-		n.ChainConfigs[chainAlias] = *chainConfig
+		n.ChainConfigs[chainAlias] = chainConfig
 	}
 
 	return nil

tests/fixture/tmpnet/node.go

@@ -98,7 +98,9 @@ func NewNode(dataDir string) *Node {
 func NewNodes(count int) []*Node {
 	nodes := make([]*Node, count)
 	for i := range nodes {
-		nodes[i] = NewNode("")
+		node := NewNode("")
+		node.EnsureKeys()
+		nodes[i] = node
 	}
 	return nodes
 }

tests/fixture/tmpnet/subnet.go

@@ -31,7 +31,7 @@ type Chain struct {
 	// Set statically
 	VMID    ids.ID
 	Config  FlagsMap
-	Genesis FlagsMap
+	Genesis []byte
 
 	// Set at runtime
 	ChainID      ids.ID
@@ -138,13 +138,9 @@ func (s *Subnet) CreateChains(ctx context.Context, w io.Writer, uri string) erro
 	}
 
 	for _, chain := range s.Chains {
-		genesisBytes, err := DefaultJSONMarshal(chain.Genesis)
-		if err != nil {
-			return fmt.Errorf("failed to marshal genesis for chain %s: %w", chain.VMID, err)
-		}
 		createChainTx, err := pWallet.IssueCreateChainTx(
 			s.SubnetID,
-			genesisBytes,
+			chain.Genesis,
 			chain.VMID,
 			nil,
 			"",