Voltmeter & pH meter rebalancing (#3336)

* voltmeter on toolbelt

You can put the voltmeter on your toolbelt

* realistic voltmeter size

See discussion in discord about why this size is reasonable.

* Update science.json

---------

Co-authored-by: Chaosvolt <chaosvolt@users.noreply.github.com>

data/json/items/tool/science.json

@@ -387,8 +387,8 @@
     "category": "tools",
     "name": { "str": "pH meter" },
     "description": "This is basically a pair of glass probes on a voltmeter.  By putting one probe into a calibration solution (conveniently included) and the other in a substance, you can calculate the acidity.",
-    "weight": "3000 g",
-    "volume": "1500 ml",
+    "weight": "500 g",
+    "volume": "750 ml",
     "price": 6000,
     "price_postapoc": 250,
     "ammo": "battery",
@@ -419,8 +419,8 @@
     "category": "tools",
     "name": { "str": "voltmeter" },
     "description": "This device has two probes that let you measure the electrical potential between two points.",
-    "weight": "3000 g",
-    "volume": "1500 ml",
+    "weight": "500 g",
+    "volume": "750 ml",
     "price": 6000,
     "price_postapoc": 250,
     "ammo": "battery",
@@ -430,6 +430,7 @@
     "symbol": ";",
     "color": "light_gray",
     "use_action": [ "REPORT_GRID_CHARGE", "REPORT_GRID_CONNECTIONS", "MODIFY_GRID_CONNECTIONS" ],
+    "flags": [ "BELT_CLIP" ],
     "magazines": [
       [
         "battery",