Add RunEndEncoded Array Support

[vustef]

Implements support for Arrow's RunEndEncoded (REE) layout as specified in the Arrow format specification. REE is a run-length encoding variant that efficiently stores arrays with repeated values using two child arrays: run_ends (indices where runs terminate) and values (the actual run values).

Implementation

• Core type: Added Arrow.RunEndEncoded{T,R,A} struct with O(log n) binary search indexing
• Type system: Registered RunEndEncodedKind in ArrowTypes module
• Serialization: Implemented arrowvector() and makenodesbuffers!() for writing REE arrays
• Deserialization: Added build() function and juliaeltype() for reading REE arrays from Arrow IPC format
• Interoperability: Validated against PyArrow-generated test files (included as fixtures)

Testing

• Cross-language validation using PyArrow 20.0.0-generated test files
• Round-trip tests for various data types (integers, floats, strings, booleans, with nulls)
• Edge cases: single runs, alternating values, long runs

Closes #476