message: Make blosc filter feature-gated in example
diff: -use hdf5::{
  - filters::{blosc_set_nthreads, Blosc},
  - {File, H5Type, Result},
  -};
  +#[cfg(feature = "blosc")]
  +use hdf5::filters::{blosc_set_nthreads, Blosc};
  +use hdf5::{File, H5Type, Result};
  use ndarray::{arr2, s};
  #[derive(H5Type, Clone, PartialEq, Debug)] // map the HDF5 type for this enum
  @@ -23,11 +22,14 @@ fn main() -> Result<()> {
  {
  let file = File::create("pixels.h5")?; // open the file for writing
  let group = file.create_group("dir")?; // create a group
  + #[cfg(feature = "blosc")]
  blosc_set_nthreads(2); // set number of threads for compressing/decompressing chunks
  - let ds = group
  - .new_dataset_builder()
  - .blosc(Blosc::ZStd, 9, true) // enable zstd compression with shuffling
  - .with_data(&arr2(&[ // write a 2-D array of data
  + let builder = group.new_dataset_builder();
  + #[cfg(feature = "blosc")]
  + let builder = builder.blosc(Blosc::ZStd, 9, true); // enable zstd compression with shuffling
  + let ds = builder
  + .with_data(&arr2(&[
  + // write a 2-D array of data
  [Pixel { xy: (1, 2), color: Color::R }, Pixel { xy: (2, 3), color: Color::B }],
  [Pixel { xy: (3, 4), color: Color::G }, Pixel { xy: (4, 5), color: Color::R }],
  [Pixel { xy: (5, 6), color: Color::B }, Pixel { xy: (6, 7), color: Color::G }],
  