perf: rewrite selling settings toggle setters only on change

on_update reran toggle_hide_tax_id, toggle_editable_rate_for_bundle_items
and toggle_discount_accounting_fields on every save, rewriting 11
property setters and clearing the meta cache of five doctypes.

Gate each toggle on has_value_changed. Fresh installs save the settings
with pure defaults (set_single_defaults), so the gated-off state must
match the JSON schema: align sales_invoice.json and
sales_invoice_item.json with the values every saved site already has —
tax_id printed when hide_tax_id is off, discount accounts hidden while
discount accounting is disabled. Packed Item rate already matches.

erpnext/accounts/doctype/sales_invoice/sales_invoice.json

@@ -297,7 +297,6 @@
    "hide_days": 1,
    "hide_seconds": 1,
    "label": "Tax Id",
-   "print_hide": 1,
    "read_only": 1
   },
   {
@@ -1940,6 +1939,7 @@
    "allow_on_submit": 1,
    "fieldname": "additional_discount_account",
    "fieldtype": "Link",
+   "hidden": 1,
    "label": "Discount Account",
    "options": "Account"
   },
@@ -2360,7 +2360,7 @@
    "link_fieldname": "consolidated_invoice"
   }
  ],
- "modified": "2026-06-21 12:46:13.250145",
+ "modified": "2026-08-11 12:00:00.000000",
  "modified_by": "Administrator",
  "module": "Accounts",
  "name": "Sales Invoice",

erpnext/accounts/doctype/sales_invoice_item/sales_invoice_item.json

@@ -887,6 +887,7 @@
    "allow_on_submit": 1,
    "fieldname": "discount_account",
    "fieldtype": "Link",
+   "hidden": 1,
    "label": "Discount Account",
    "options": "Account"
   },
@@ -1067,7 +1068,7 @@
  "idx": 1,
  "istable": 1,
  "links": [],
- "modified": "2026-08-07 17:31:31.732720",
+ "modified": "2026-08-11 12:00:00.000000",
  "modified_by": "Administrator",
  "module": "Accounts",
  "name": "Sales Invoice Item",

erpnext/selling/doctype/selling_settings/selling_settings.py

@@ -125,6 +125,9 @@ class SellingSettings(Document):
 			)
 
 	def toggle_hide_tax_id(self):
+		if not self.has_value_changed("hide_tax_id"):
+			return
+
 		_hide_tax_id = cint(self.hide_tax_id)
 
 		# Make property setters to hide tax_id fields
@@ -137,6 +140,9 @@ class SellingSettings(Document):
 			)
 
 	def toggle_editable_rate_for_bundle_items(self):
+		if not self.has_value_changed("editable_bundle_item_rates"):
+			return
+
 		editable_bundle_item_rates = cint(self.editable_bundle_item_rates)
 
 		make_property_setter(
@@ -149,6 +155,9 @@ class SellingSettings(Document):
 		)
 
 	def toggle_discount_accounting_fields(self):
+		if not self.has_value_changed("enable_discount_accounting"):
+			return
+
 		enable_discount_accounting = cint(self.enable_discount_accounting)
 
 		make_property_setter(