Add binary I/O header for sampling profiler

Defines the API and data structures for a high-performance binary
format for profiling data. The format uses string/frame deduplication,
varint encoding, and delta compression to achieve 10-50x size reduction
compared to text formats. Optional zstd compression provides additional
savings.

The header includes inline varint encode/decode functions since these
are called in tight loops during both writing and reading. Structures
for both writer (BinaryWriter) and reader (BinaryReader) are defined
here to allow the module.c bindings to allocate them.

Author: pablogsal