Add test coverage for HDF5 compression in EmpCylSL disk cache

[Copilot]

Addresses feedback requesting test coverage for the HDF5 compression functionality added to EmpCylSL disk cache files.

Test Suite (tests/Disk/cyl_compression_test.py)

Six test cases covering:

• Compression enable/disable: Verifies compress: 0 through compress: 9 parameter handling
• Data integrity: Validates compressed cache files read back correctly across basis instances
• Level validation: Tests in-range (0-9) and out-of-range (clamped to 9) compression levels
• Shuffle filter: Verifies byte shuffle filter operates with compression (enabled by default)
• Compression effectiveness: Compares file sizes to demonstrate compression ratio

# Example usage in YAML config
disk_config = """
parameters:
  ...
  eof_file: .eof.cache.compressed
  compress: 5  # Gzip level 0-9, 0=disabled
"""
basis = pyEXP.basis.Basis.factory(disk_config)

Integration

• Added pyexpCylCompressionTest to CMake test suite (labeled long)
• Test documentation in tests/Disk/README.md with implementation references
• Updated .gitignore for Python cache artifacts

Run via: ctest -R pyexpCylCompressionTest

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