Optimize Software Fallback Path with ISA-L Integration

### Summary
Currently, zlib-accel provides hardware acceleration through QAT and IAA with fallback to standard zlib software implementation. This creates a significant performance gap when hardware acceleration is unavailable. We propose integrating Intel ISA-L (Intelligent Storage Acceleration Library) as an intermediate performance layer to optimize the software fallback path.
### Background
Zlib-accel's current fallback hierarchy:

1. Hardware acceleration (QAT/IAA) - Best performance
2. Software zlib - Standard performance with significant gap from hardware

The performance drop when falling back to software zlib can be substantial, potentially negating the benefits of using zlib-accel in mixed workload scenarios or systems without available hardware accelerators.
### Proposed Solution
Integrate ISA-L's optimized compression implementation as an intermediate fallback layer:

1. Hardware acceleration (QAT/IAA) - Best performance
2. ISA-L optimized software - Enhanced performance using SIMD instructions
3. Standard zlib - Compatibility fallback

### Benefits

- Reduced performance gap: ISA-L can provide significant performance improvement over standard zlib
- Broader acceleration coverage: Systems without QAT/IAA still benefit from optimized compression
- Consistency: Better performance consistency across different hardware configurations
- Maintained compatibility: ISA-L maintains zlib API compatibility

### Implementation Considerations

- Fallback logic: Modify the current fallback mechanism to include ISA-L as intermediate layer
- Configuration options: Allow users to configure fallback preferences
- Performance profiling: Benchmark ISA-L performance across different workloads

### Questions for Discussion

1. Should ISA-L integration be optional (compile-time flag) or always included?
2. Should there be configuration options to skip ISA-L and fall directly to standard zlib?

### References
[ISA-L igzip implementation](https://github.com/intel/isa-l/tree/master/igzip/shim)

### Expected Impact
This enhancement would make zlib-accel more attractive for deployment in heterogeneous environments and provide consistent performance benefits even when hardware acceleration is unavailable, ultimately improving the overall value proposition of the library.