Replace Float 'nan' with None for modbus floats (#93832)

Co-authored-by: jan iversen <jancasacondor@gmail.com>

homeassistant/components/modbus/base_platform.py

@@ -218,6 +218,9 @@ def unpack_structure_result(self, registers: list[int]) -> str | None:
                 # the conversion only when it's absolutely necessary.
                 if isinstance(v_temp, int) and self._precision == 0:
                     v_result.append(str(v_temp))
+                elif v_temp != v_temp:  # noqa: PLR0124
+                    # NaN float detection replace with None
+                    v_result.append("nan")  # pragma: no cover
                 else:
                     v_result.append(f"{float(v_temp):.{self._precision}f}")
             return ",".join(map(str, v_result))
@@ -228,6 +231,10 @@ def unpack_structure_result(self, registers: list[int]) -> str | None:
         # We could convert int to float, and the code would still work; however
         # we lose some precision, and unit tests will fail. Therefore, we do
         # the conversion only when it's absolutely necessary.
+
+        # NaN float detection replace with None
+        if val_result != val_result:  # noqa: PLR0124
+            return None  # pragma: no cover
         if isinstance(val_result, int) and self._precision == 0:
             return str(val_result)
         if isinstance(val_result, str):