[LibBlosc] BREAKING use compcode int instead of string as a field

[nhz2]

The plan is for this to be the last API break for LibBlosc, with a 1.0 released sometime next week. @icweaver and @eschnett no code changes are needed in ASDF.jl (but let me know if you want any other breaking API change before the 1.0 release).

[codecov]

Codecov Report

❌ Patch coverage is 92.30769% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 93.75%. Comparing base (58a7da7) to head (b590552).

Files with missing lines	Patch %	Lines
LibBlosc/src/libblosc.jl	84.61%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #95      +/-   ##
==========================================
- Coverage   97.53%   93.75%   -3.79%     
==========================================
  Files           4        4              
  Lines          81       80       -1     
==========================================
- Hits           79       75       -4     
- Misses          2        5       +3     

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