move volume and weight vals to math

[GuardianDll]

Summary

None

Purpose of change

Since #76892 allow to use math evaluation on items, that means we can just add math function that allow us to directly check whatever we need, in all possible ways

Describe the solution

This PR replaces old u_val('weight') and u_val('volume') with math syntax, that allow to be used on items. For volume it also adds abiltiy to read character volume

Testing

test json

  {
    "type": "effect_on_condition",
    "id": "AAAAAAAA",
    "effect": [
      {
        "u_run_inv_eocs": "manual_mult",
        "true_eocs": [
          {
            "id": "EOC_WHATEVER_0",
            "effect": [
              { "math": [ "_u", "=", "u_weight()" ] },
              { "math": [ "_n", "=", "n_weight()" ] },
              {
                "u_message": "alpha: <u_name>, weight <context_val:u> mg, beta: <npc_name>, weight <context_val:n> mg"
              }
            ]
          }
        ]
      }
    ]
  },
  {
    "type": "effect_on_condition",
    "id": "BBBBBBBB",
    "effect": [
      {
        "u_run_inv_eocs": "manual_mult",
        "true_eocs": [
          {
            "id": "EOC_WHATEVER_1",
            "effect": [
              { "math": [ "_u", "=", "u_volume()" ] },
              { "math": [ "_n", "=", "n_volume()" ] },
              {
                "u_message": "alpha: <u_name>, volume <context_val:u> ml, beta: <npc_name>, volume <context_val:n> ml"
              }
            ]
          }
        ]
      }
    ]
  },

Additional context

i would really like to also add the field similar to time() funciton, but #70996 uses some magic i am not familiar with