♻️ refactor lua_push_interface and add json module

Refactor pushInterfaceToLua to delegate unsupported types (nil, bool/int/float/string/map/slice) recursively via new lvalueFromInterface helper. Simplify typed slice and map handlers, remove explicit nil case (now handled by lvalueFromInterface), eliminate redundant type switches in pushMapStringIntToLua and similar functions. Add new luajson.go with RegisterJSON, lua.JSONEncode/Decode bindings using lvalueFromInterface and Table2 Interface for bidirectional round-trips. Include comprehensive tests covering scalars, nested structures (e.g., kmindex response), arrays and error cases.

pkg/obilua/luajson.go

@@ -0,0 +1,71 @@
+package obilua
+
+import (
+	"encoding/json"
+
+	lua "github.com/yuin/gopher-lua"
+)
+
+// RegisterJSON registers the json module in the Lua state as a global,
+// consistent with obicontext, BioSequence, and http.
+//
+// Exposes:
+//
+//	json.encode(data)   → string         (on success)
+//	json.encode(data)   → nil, err       (on error)
+//	json.decode(string) → value          (on success)
+//	json.decode(string) → nil, err       (on error)
+func RegisterJSON(luaState *lua.LState) {
+	table := luaState.NewTable()
+	luaState.SetField(table, "encode", luaState.NewFunction(luaJSONEncode))
+	luaState.SetField(table, "decode", luaState.NewFunction(luaJSONDecode))
+	luaState.SetGlobal("json", table)
+}
+
+// luaJSONEncode implements json.encode(data) for Lua.
+func luaJSONEncode(L *lua.LState) int {
+	val := L.CheckAny(1)
+
+	var goVal interface{}
+	switch v := val.(type) {
+	case *lua.LTable:
+		goVal = Table2Interface(L, v)
+	case lua.LString:
+		goVal = string(v)
+	case lua.LNumber:
+		goVal = float64(v)
+	case lua.LBool:
+		goVal = bool(v)
+	case *lua.LNilType:
+		goVal = nil
+	default:
+		L.Push(lua.LNil)
+		L.Push(lua.LString("json.encode: unsupported type"))
+		return 2
+	}
+
+	b, err := json.Marshal(goVal)
+	if err != nil {
+		L.Push(lua.LNil)
+		L.Push(lua.LString(err.Error()))
+		return 2
+	}
+
+	L.Push(lua.LString(b))
+	return 1
+}
+
+// luaJSONDecode implements json.decode(string) for Lua.
+func luaJSONDecode(L *lua.LState) int {
+	s := L.CheckString(1)
+
+	var goVal interface{}
+	if err := json.Unmarshal([]byte(s), &goVal); err != nil {
+		L.Push(lua.LNil)
+		L.Push(lua.LString(err.Error()))
+		return 2
+	}
+
+	pushInterfaceToLua(L, goVal)
+	return 1
+}