Ensure BlankNodes are handled for HDT files created with hdt-java

[donpellegrino]

Describe the bug
hdt-cpp and hdt-java use different naming patterns for blank node IDs. The initial support for blank nodes works for hdt-cpp but not for hdt-java. This issue is to ensure support for blank node IDs as generated by hdt-java when using its CLI tools to make an HDT file (e.g., rdf2hdt.sh instead of rdf2hdt.)

To Reproduce
Steps to reproduce the behavior:

1. Run the oxhdt test suite.
2. Observe failures for the cases where HDT Java was used to create the HDT files. Note that this was done to work around the cases where HDT C++ did not support the input RDF syntax for those cases from the W3C test suite.

[GregHanson]

Opened issue in in hdt-java repo:
rdfhdt/hdt-java#210

[GregHanson]

alternative to the above, can also add | '\u{0040}' (UTF8 rep for @) to the oxigraph code here and all tests pass:

https://github.com/oxigraph/oxigraph/blob/main/lib/oxrdf/src/blank_node.rs#L275