feat: introduce type casting executors for schema evolution

[lszskye]

Introduce Type Casting Executors for Schema Evolution

Summary

Add a set of CastExecutor implementations under src/paimon/core/casting/ to support type casting between boolean, numeric, decimal, and string types. These executors are essential for schema evolution scenarios where column types change across table versions, enabling predicate pushdown and data reading to work correctly across different schemas.

Each executor supports two casting modes:

• Literal casting: Converts a single Literal value to the target type (used during predicate rewriting).
• Array casting: Converts an entire Arrow Array to the target type (used during batch data reading).

New Classes

BooleanToDecimalCastExecutor — Casts boolean values to decimal types. Converts true to Decimal128(1) and false to Decimal128(0) with the specified target precision and scale.

BooleanToNumericCastExecutor — Casts boolean values to numeric primitive types (int8, int16, int32, int64, float, double). Uses a dispatch map to route casting logic per target FieldType, mapping true to 1 and false to 0.

BooleanToStringCastExecutor — Casts boolean values to string type. Converts true to "true" and false to "false".

DecimalToDecimalCastExecutor — Casts decimal values between different precision/scale decimal types. Handles rescaling by adjusting the underlying Decimal128 representation to match the target precision and scale, with overflow detection.

DecimalToNumericPrimitiveCastExecutor — Casts decimal values to numeric primitive types. Truncates the decimal value to the target integer or floating-point type by dividing out the scale factor.

NumericPrimitiveToDecimalCastExecutor — Casts numeric primitive values (int8 through double) to decimal types. Employs templated dispatch to handle each source type, scaling the input value to the target decimal precision and scale.

NumericToBooleanCastExecutor — Casts numeric values to boolean type. Uses a dispatch map per source FieldType, converting zero values to false and non-zero values to true.

NumericToStringCastExecutor — Casts numeric values to string type. Uses a dispatch map per source FieldType, converting each numeric value to its string representation.

StringToBooleanCastExecutor — Casts string values to boolean type. Recognizes "true"/"TRUE" as true and "false"/"FALSE" as false, returning an error for unrecognized string values.

StringToDecimalCastExecutor — Casts string values to decimal types. Parses the string into an arrow::Decimal128 value with the specified target precision and scale, with support for null propagation when parsing fails.

StringToNumericPrimitiveCastExecutor — Casts string values to numeric primitive types (int8 through double). Uses a templated dispatch map per target FieldType, parsing the string representation into the corresponding numeric value.