Introduce separate _BatchSize (min) and _BatchSizeMax (max) constants to replace the single _BatchSize variable. Update RebatchBySize to accept both maxBytes and maxCount parameters, flushing when either limit is exceeded. Set default batch size min to 1, max to 2000, and memory limit to 128 MB. Update CLI options and sequence_reader.go accordingly.
Implement memory-aware batch sizing with --batch-mem CLI option, enabling adaptive batching based on estimated sequence memory footprint. Key changes:
- Added _BatchMem and related getters/setters in pkg/obidefault
- Implemented RebatchBySize() in pkg/obiter for memory-constrained batching
- Added BioSequence.MemorySize() for conservative memory estimation
- Integrated batch-mem option in pkg/obioptions with human-readable size parsing (e.g., 128K, 64M, 1G)
- Added obiutils.ParseMemSize/FormatMemSize for unit conversion
- Enhanced pool GC in pkg/obiseq/pool.go to trigger explicit GC for large slice discards
- Updated sequence_reader.go to apply memory-based rebatching when enabled
