Inherit OverfloFix and QuantizationPreset from StrEnum (#2608)

### Changes

- Inherit `OverflowFix` and `QuantizationPreset` from `StrEnum` instead
of `Enum` to make them serializable.
- Expose `OverflowFix` as `nncf.OverflowFix`

### Reason for changes

Came up during optimum-intel integration.

nncf/__init__.py

@@ -46,6 +46,7 @@
     AdvancedAccuracyRestorerParameters as AdvancedAccuracyRestorerParameters,
 )
 from nncf.quantization.advanced_parameters import AdvancedQuantizationParameters as AdvancedQuantizationParameters
+from nncf.quantization.advanced_parameters import OverflowFix as OverflowFix
 from nncf.scopes import IgnoredScope as IgnoredScope
 from nncf.scopes import Subgraph as Subgraph
 from nncf.version import __version__ as __version__

nncf/common/quantization/structs.py

@@ -19,6 +19,7 @@
 from nncf.common.utils.api_marker import api
 from nncf.config.schemata.defaults import QUANTIZATION_BITS
 from nncf.config.schemata.defaults import QUANTIZATION_PER_CHANNEL
+from nncf.parameters import StrEnum
 from nncf.parameters import TargetDevice
 
 
@@ -327,7 +328,7 @@ class UnifiedScaleType(Enum):
 
 
 @api(canonical_alias="nncf.QuantizationPreset")
-class QuantizationPreset(Enum):
+class QuantizationPreset(StrEnum):
     """
     An enum with values corresponding to the available quantization presets.
     """

nncf/quantization/advanced_parameters.py

@@ -22,13 +22,14 @@
 import nncf
 from nncf.common.quantization.structs import QuantizationScheme as QuantizationMode
 from nncf.common.utils.api_marker import api
+from nncf.parameters import StrEnum
 from nncf.quantization.range_estimator import AggregatorType
 from nncf.quantization.range_estimator import RangeEstimatorParameters
 from nncf.quantization.range_estimator import StatisticsType
 
 
-@api()
-class OverflowFix(Enum):
+@api(canonical_alias="nncf.OverflowFix")
+class OverflowFix(StrEnum):
     """
     This option controls whether to apply the overflow issue fix for the 8-bit
     quantization.