Only apply HDF5 shuffle filter when compression is enabled

[Copilot]

The shuffle filter was being applied based solely on the H5shuffle flag, without verifying compression was enabled. This added unnecessary overhead when H5compress=0 and H5szip=false.

Changes

• EmpCylSL.cc: Changed condition from if (H5compress) to if (H5compress > 0 || H5szip) to support both Deflate and Szip compression modes
• BiorthBasis.cc: Updated three compression sections:
  • Sample stats: Deflate-only with if (H5compress > 0)
  • Coefficients/covariance: Both compression types with if (H5compress > 0 || H5szip)
• Added comments clarifying that shuffle is only applied when the outer condition guarantees compression is enabled

Behavior

Before:

if (H5compress) {
  if (H5shuffle) dcpl.add(HighFive::Shuffle());
  // Always applies shuffle when H5shuffle=true and H5compress!=0
}

After:

if (H5compress > 0 || H5szip) {
  // Only apply shuffle filter when compression is enabled (guaranteed by outer if)
  if (H5shuffle) dcpl.add(HighFive::Shuffle());
  // Shuffle only applies when Deflate (H5compress>0) or Szip is enabled
}

This prevents shuffle overhead when compression is disabled while allowing Szip to be used independently of the H5compress level setting.

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