Parenthesis-delimited blocks (@article(...)) are silently parsed as implicit comments

[MiWeiss]

Standard BibTeX allows parentheses as block delimiters, but the splitter regex only accepts { (bibtexparser/splitter.py:296, (?={) lookahead). A block like

@article(test2002, author = {A}, year = {2002})

becomes an ImplicitComment — no entry, no failed block, no warning. Silent data loss.

Either support the (...) form, or at minimum emit a ParsingFailedBlock so the loss is visible.

[claell]

I opened draft PR #571 using the fail-closed option discussed here: parenthesis-delimited blocks are retained as explicit parsing failures, with recovery for subsequent supported blocks. It does not claim full parenthesis parsing support.