Memory-aware Batching and Static Linux Builds

### Memory-Aware Batching
- Replaced single batch size limits with configurable min/max bounds and memory limits for more precise control over resource usage.
- Added `--batch-mem` CLI option to enable adaptive batching based on estimated sequence memory footprint (e.g., 128K, 64M, 1G).
- Introduced `RebatchBySize()` with explicit support for both byte and count limits, flushing when either threshold is exceeded.
- Implemented conservative memory estimation via `BioSequence.MemorySize()` and enhanced garbage collection to trigger explicit cleanup after large batch discards.
- Updated internal batching logic across `batchiterator.go`, `fragment.go`, and `obirefidx.go` to consistently use default memory (128 MB) and size (min: 1, max: 2000) bounds.

### Linux Build Enhancements
- Enabled static linking for Linux binaries using musl, producing portable, self-contained executables without external dependencies.

### Notes
- This release consolidates and improves batching behavior introduced in 4.4.20, with no breaking changes to the public API.
- All user-facing batching behavior is now governed by consistent memory and count constraints, improving predictability and stability during large dataset processing.

pkg/obioptions/version.go

@@ -3,7 +3,7 @@ package obioptions
 // Version is automatically updated by the Makefile from version.txt
 // The patch number (third digit) is incremented on each push to the repository
 
-var _Version = "Release 4.4.21"
+var _Version = "Release 4.4.22"
 
 // Version returns the version of the obitools package.
 //

version.txt

@@ -1 +1 @@
-4.4.21
+4.4.22