Changes from 2.6.1 to 2.7.1

• Caterva has been merged and carefully integrated in C-Blosc2 in the new b2nd interface.
  For more info on the new interface, see https://www.blosc.org/c-blosc2/reference/b2nd.html.
  Thanks to Marta Iborra, Oscar Guiñón, J. David Ibáñez and Francesc Alted. Also thanks to
  Aleix Alcacer for his great work in the Caterva project.

  We have a blog about this: https://www.blosc.org/posts/blosc2-ndim-intro

• Updated internal zstd sources to 1.5.4. Thanks to Dimitri Papadopoulos.

• blosc2_schunk_avoid_cframe_free and blosc2_schunk_append_file are exported as public functions now.
  Thanks to @bnavigator.

• BloscLZ codec is now treated exactly the same as LZ4. Before BloscLZ was considered less capable of reaching
  decent compression ratios, but this has changed quite a bit lately, so there is no point in treating both differently.

• Fixed some leaks, mainly on the test suite.

• Fixed quite a bit of compiler warnings.