Fix: Allow 'value' to be used outside of enums by separating exception words.

[xioxin]

In the upgrade to 3.0.1, I found that the value field in the model was changed to $value. However, value is not a reserved word in Dart.

@JsonSerializable(explicitToJson: true)
class StatisticalLabel {
  const EnrollStatisticsLabel({
    required this.describe,
    required this.$value,
    this.unit,
  });

  @JsonKey(name: 'describe')
  final String describe;
  @JsonKey(name: 'value')
  final String $value;
  @JsonKey(name: 'unit')
  final String? unit;
....

Upon checking the code, I discovered that #716 added value to exceptionWords to resolve conflicts with the value parameter in enums.

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I added exceptionWordsInEnum to ensure that value is treated as an exception only within enums.