nix: partial switch to explicit pname/version

Switch to pname/version parsing (instead of splitting name into
these) for specific case of "{name}-unstable-{ver}". Before,
"unstable" was parsed as a part of the package name, while it belongs
to version in most cases. This reduces diff for following steps of
switching to pname/version.

Author: AMDmi3

repology/parsers/parsers/nix.py

@@ -186,6 +186,8 @@ def iter_parse(self, path: str, factory: PackageFactory) -> Iterable[PackageMake
                 if match is None:
                     pkg.log('cannot parse name "{}"'.format(packagedata['name']), severity=Logger.ERROR)
                     continue
+                elif match.group(1).endswith('-unstable') and version.startswith('unstable-') and match.group(1)[:-9] == pname and match.group(2) == version[9:]:
+                    pass
                 else:
                     pname = match.group(1)
                     version = match.group(2)