fix(lua) avoid LuaJIT issue with FFI callback roundtrips

The Kong Gateway CI started seeing intermittent crashes with "bad callback" errors:

See:
https://luajit.freelists.narkive.com/sdhSLJSr/how-to-make-bad-callback-more-deterministic
```
The bad callback error happens because some JIT-compiled Lua code calls a C
function which in turn calls an FFI callback.
```

https://lua-l.lua.narkive.com/qXJrNlpP/luajit-ffi-windows-bad-callback-error-in-msgwaitformultipleobjects-proof-of-concept
From Mike Pall:
```
The problem is that a FFI callback cannot safely be called from a
C function which is itself called via the FFI from JIT-compiled
code. In your case this is the call to MsgWaitForMultipleObjects.

I've put in a lot of heuristics to detect this, and it usually
succeeds in disabling compilation for such a function. However in
your case the loop is compiled before the callback is ever called,
so the detection fails.

The straighforward solution is to put the message loop into an
extra Lua function and use jit.off(func)
```

See

lib/resty/wasmx/proxy_wasm.lua

@@ -113,7 +113,9 @@ do
             lval = ffi_str(cvalue.data, cvalue.len)
         end
 
+        jit.off()
         local pok, ok, lvalue, is_const = pcall(lua_prop_setter, lkey, lval)
+        jit.on()
         if not pok then
             ngx.log(ngx.ERR, "error setting property from Lua: ", ok)
             return FFI_ERROR
@@ -133,7 +135,9 @@ do
                                                                  cvalue)
         local lkey = ffi_str(ckey.data, ckey.len)
 
+        jit.off()
         local pok, ok, lvalue, is_const = pcall(lua_prop_getter, lkey)
+        jit.on()
         if not pok then
             ngx.log(ngx.ERR, "error getting property from Lua: ", ok)
             return FFI_ERROR