Fix drivers modifying memory during set_memory()

This has been a warning for a while, so most of the popular drivers
are fixed by now. This fixes the two remaining (obvious) ones and adds
a test to prevent more from being added.

Note that there may be some that still only modify the memory in
edge cases that this test doesn't cover.

chirp/drivers/tk270.py

@@ -645,11 +645,7 @@ class Kenwood_P60_Radio(chirp_common.CloneModeRadio, chirp_common.ExperimentalRa
         self.encode_tone(_mem.tx_tone, txmode, txtone, txpol)
         self.encode_tone(_mem.rx_tone, rxmode, rxtone, rxpol)
 
-        # power, default power is high, as the low is configurable via a key
-        if mem.power is None:
-            mem.power = POWER_LEVELS[1]
-
-        _mem.power = POWER_LEVELS.index(mem.power)
+        _mem.power = POWER_LEVELS.index(mem.power or POWER_LEVELS[1])
 
         # skip
         self.set_scan(mem.number - 1, mem.skip)

chirp/drivers/tk760g.py

@@ -1073,12 +1073,7 @@ class Kenwood_Series_60G(chirp_common.CloneModeRadio,
             except IndexError:
                 _mem.name[i] = "\x20"
 
-        # power
-        # default power is low
-        if mem.power is None:
-            mem.power = POWER_LEVELS[0]
-
-        _mem.power = POWER_LEVELS.index(mem.power)
+        _mem.power = POWER_LEVELS.index(mem.power or POWER_LEVELS[0])
 
         # wide/marrow
         _mem.wide = MODES.index(mem.mode)

chirp/drivers/vx1.py

@@ -866,17 +866,18 @@ class VX1RadioCG1(VX1Radio):
         return mem
 
     def set_memory(self, mem):
-        if isinstance(mem.number, str):
+        number = mem.number
+        if isinstance(number, str):
             # Convert string to number
-            mem.number = self.SPECIAL_MEMORIES[mem.number]
+            number = self.SPECIAL_MEMORIES[mem.number]
 
         # Map CG1 subdevice number to cg1_idx
-        if mem.number <= 72:
+        if number <= 72:
             # Regular and L/U memories: 1-72 map to cg1_idx 8-79
-            cg1_idx = mem.number + 7
+            cg1_idx = number + 7
         else:
             # Home channels: 73-80 map to cg1_idx 0-7
-            cg1_idx = mem.number - 73
+            cg1_idx = number - 73
 
         # Handle CG1 memory structure directly
         _mem = self._memobj.cg1_memory[cg1_idx]

tests/test_edges.py

@@ -37,6 +37,10 @@ class TestCaseEdges(base.DriverTest):
             n = self.radio.get_memory(m.number)
             self.assertEqualMem(m, n)
 
+    def test_set_does_not_modify_input(self):
+        m = self.get_mem()
+        self.radio.set_memory(chirp_common.FrozenMemory(m))
+
     def test_bandedges(self):
         m = self.get_mem()
         min_step = min(self.rf.has_tuning_step and