v4.0.0

• Rebuilt the public API around reusable codec classes such as
  DecimalCodec, CompactCodec, PercentCodec,
  BytesCodec, and CurrencyCodec.
• Added reusable immutable codecs with standard encode/decode support and
  readable format, parse, and tryParse aliases.
• Added direct parsing support for decimal numbers, compact suffixes,
  percentages, byte sizes, and display currency values.
• Added decimal and binary byte codecs.
• Added reusable NumeralUnit / NumeralUnitSet models for unit-based codecs.
• Added custom number style support for unit-style codecs, allowing currency,
  percentage, byte, and compact formats to compose with language-specific
  number codecs.
• Added extension.dart for fluent one-off formatting, such as
  12345.compact(), 1536.bytes(binary: true), and 123.currency(r'$').
• Added built-in en.dart and zh.dart language paths with locale-specific
  compact units, including Simplified Chinese cardinal, year, financial
  numeral, and RMB uppercase amount formatting and parsing.
• Removed the old num.numeral() / beautiful extension API.