fix(lws): serialize XMR/WOW atomic amounts as strings (u64 > 2^53 safe)

XMR/WOW atomic amounts (piconero/wownoshi) can exceed 2^53, which a
JavaScript number cannot hold exactly, so a large balance or output was
silently rounded when the wallet JSON.parsed it. Serialize every atomic
amount (balance total_received/locked/pending, spent + unspent output
amounts, history totals) as a decimal string; heights, indices, counts,
and fee params stay numbers. utoipa value_type=String keeps the OpenAPI
honest. Tests assert the string wire contract for a 2^53+1 value.

openapi.json

@@ -3728,15 +3728,11 @@
             "minimum": 0
           },
           "locked_balance": {
-            "type": "integer",
-            "format": "int64",
-            "minimum": 0
+            "type": "string"
           },
           "pending_balance": {
-            "type": "integer",
-            "format": "int64",
-            "description": "Unconfirmed (mempool) received — 0-conf. `0` until the LWS reports mempool\nrows (the monero-lws mempool feature); never negative.",
-            "minimum": 0
+            "type": "string",
+            "description": "Unconfirmed (mempool) received — 0-conf. `0` until the LWS reports mempool\nrows (the monero-lws mempool feature); never negative."
           },
           "scanned_height": {
             "type": "integer",
@@ -3756,9 +3752,8 @@
             "minimum": 0
           },
           "total_received": {
-            "type": "integer",
-            "format": "int64",
-            "minimum": 0
+            "type": "string",
+            "example": "12345000000000"
           },
           "transaction_count": {
             "type": "integer",
@@ -4626,9 +4621,7 @@
         ],
         "properties": {
           "amount": {
-            "type": "integer",
-            "format": "int64",
-            "minimum": 0
+            "type": "string"
           },
           "key_image": {
             "type": "string"
@@ -4742,15 +4735,11 @@
             "type": "string"
           },
           "total_received": {
-            "type": "integer",
-            "format": "int64",
-            "minimum": 0
+            "type": "string"
           },
           "total_sent": {
-            "type": "integer",
-            "format": "int64",
-            "description": "\"Possible\" sent — candidate spends, not authoritative.",
-            "minimum": 0
+            "type": "string",
+            "description": "\"Possible\" sent — candidate spends, not authoritative."
           },
           "unlock_time": {
             "type": "integer",
@@ -4776,9 +4765,7 @@
         ],
         "properties": {
           "amount": {
-            "type": "integer",
-            "format": "int64",
-            "minimum": 0
+            "type": "string"
           },
           "global_index": {
             "type": "integer",