feat: embed genesis.json for known Sei chains

Embed genesis data for pacific-1, atlantic-2, and arctic-1 via
go:embed, removing any need to fetch genesis over the network or
from S3 for well-known chains.

Provides GenesisForChain(chainID) to retrieve the embedded bytes,
KnownChain(chainID) for chain metadata (RPC URL, genesis time), and
KnownChainIDs() to enumerate supported chains.

Unknown chain IDs return an error, requiring the caller to supply
their own genesis source.

Author: bdchatham

chains.go

@@ -0,0 +1,67 @@
+package seiconfig
+
+import (
+	"embed"
+	"fmt"
+	"path"
+)
+
+//go:embed chains/*/genesis.json
+var chainFS embed.FS
+
+// ChainInfo describes a well-known Sei network whose genesis is embedded in
+// this binary. Callers that need a chain not listed here must supply their own
+// genesis configuration.
+type ChainInfo struct {
+	ChainID     string
+	RPC         string
+	GenesisTime string
+}
+
+// knownChains is the authoritative set of chains with embedded genesis data.
+var knownChains = map[string]ChainInfo{
+	"pacific-1": {
+		ChainID:     "pacific-1",
+		RPC:         "https://rpc.sei-apis.com",
+		GenesisTime: "2023-05-22T15:00:00Z",
+	},
+	"atlantic-2": {
+		ChainID:     "atlantic-2",
+		RPC:         "https://rpc-testnet.sei-apis.com",
+		GenesisTime: "2023-02-24T01:00:00Z",
+	},
+	"arctic-1": {
+		ChainID:     "arctic-1",
+		RPC:         "https://rpc-arctic-1.sei-apis.com",
+		GenesisTime: "2024-01-25T20:18:30.242526108Z",
+	},
+}
+
+// KnownChain returns metadata for a well-known chain, or nil if the chain ID
+// is not recognised.
+func KnownChain(chainID string) *ChainInfo {
+	info, ok := knownChains[chainID]
+	if !ok {
+		return nil
+	}
+	return &info
+}
+
+// KnownChainIDs returns the set of chain IDs that have embedded genesis data.
+func KnownChainIDs() []string {
+	ids := make([]string, 0, len(knownChains))
+	for id := range knownChains {
+		ids = append(ids, id)
+	}
+	return ids
+}
+
+// GenesisForChain returns the embedded genesis.json bytes for a well-known
+// chain. Returns an error if the chain ID is not recognised — the caller must
+// provide their own genesis source for unknown chains.
+func GenesisForChain(chainID string) ([]byte, error) {
+	if _, ok := knownChains[chainID]; !ok {
+		return nil, fmt.Errorf("unknown chain %q: provide a custom genesis source", chainID)
+	}
+	return chainFS.ReadFile(path.Join("chains", chainID, "genesis.json"))
+}