feat(node): store state for any # of networks

Addresses kindelia#163

Previously chain state was stored under a path such as:

    ~/.kindelia/state/{blocks,heaps}

With this change, the data is stored at:

    ~/.kindelia/state/<network_id>/{blocks,heaps}

This enables for example flipping back and forth between a testnet
and mainnet just by changing network_id in the config, or even via
cli arg.

kindelia/src/main.rs

@@ -236,7 +236,7 @@ pub fn run_cli() -> anyhow::Result<()> {
 
       let network_id = resolve_cfg!(
         env = "KINDELIA_NETWORK_ID",
-        prop = "node.network.network_id".to_string(),
+        prop = "node.network.network_id",
         no_default = anyhow!("Missing `network_id` parameter."),
         cli_val = network_id,
         cfg = config,