…ateBuilder

- Add ColumnType final class with 25 fixed-type constants (TINYINT through
  UUID), 7 parameterised factory methods (varChar, charType, decimal,
  numeric, binary, varBinary, timestamp), and 4 chainable modifier methods
  (notNull, unique, autoIncrement, defaultValue)
- Add CreateBuilder.column(String, ColumnType) overload; delegates to the
  existing column(String, String) via ColumnType.toSql() — fully backward
  compatible
- Add ColumnTypeTest: 32 tests covering constants, factories, modifiers,
  chaining, and CreateBuilder integration

…reference

- Replace minimal example with full ColumnType-based table definition
- Add ColumnType section: fixed-type constant table, parameterised factory
  method table, modifier chain table, and custom-type examples
- Expand IF NOT EXISTS and composite-PK examples to use ColumnType
- Update method reference table to include column(String, ColumnType)

Each class in the new col package wraps a single ColumnType constant or
factory method behind a concise name and a uniform of() / of(params)
factory. Developers can use a wildcard import to write:

    import com.github.ezframework.javaquerybuilder.query.builder.col.*;

    .column("id",         Int.of().notNull().autoIncrement())
    .column("username",   VarChar.of(64).notNull().unique())
    .column("price",      Decimal.of(10, 2))
    .column("created_at", Timestamp.of())

instead of prefixing every type with ColumnType.

Classes added (31 total):
  Fixed types: TinyInt, SmallInt, Int, BigInt, SqlFloat, SqlDouble,
    Real, Bool, Text, TinyText, MediumText, LongText, Clob,
    Blob, TinyBlob, MediumBlob, LongBlob, Date, Time, DateTime,
    Json, Serial, BigSerial, Uuid
  Parameterised types: Timestamp (overloaded of() / of(int)),
    VarChar, Char, Decimal, Numeric, Binary, VarBinary

  - SqlFloat / SqlDouble / Bool named to avoid shadowing java.lang types
    when the package is wildcard-imported
  - ColTypesTest: 34 tests covering all classes and modifier chaining