Add blosc_compress_ctx() and blosc_decompress_ctx() for Blosc1 compatibility

[FrancescAlted]

The initial plan was to deprecate blosc_compress_ctx() and blosc_decompress_ctx() in favor of the newer blosc2_compress_ctx() and blosc2_decompress_ctx(). However, as there is no deprecation warning in docs of the original blosc_compress_ctx() and blosc_decompress_ctx() for Blosc1, we should provide an implementation for these (probably as thin wrappers of blosc2_compress_ctx() and blosc2_decompress_ctx() ) for Blosc2.