Fix serializer round-trip and robustness bugs (backslash, timezone, date-shaped ids, QName typing, out-of-range ints, anonymous nodes)

[amateescu]

Changes

• Reject qualified-name local parts containing a backslash when emitting PROV-N and PROV-JSON. PN_CHARS_ESC has no escape for backslash, so decode() cannot tell it from an escaped mark and the name would alias a different one on round trip. The check rides QualifiedNameEscaper::escape()'s existing scan.
• Parse timezone-less xsd:dateTime values as UTC in the PROV-N, JSON, and XML deserializers, so a document's content no longer depends on the server's default timezone.
• Treat a date-shaped PROV-N token as a malformed dateTime only when it sits in a formal time slot; a default-namespace identifier such as 2024-01-15-report now round-trips.
• Validate PROV-JSON section shapes and throw DeserializationException for a scalar where a map is expected, instead of a raw TypeError or a silent zero-record parse.
• Sign integers outside the 32-bit range as xsd:long in ValueIdentity, matching the serializers, so such a value and its Literal::long() equivalent dedupe and compare as equal.
• Advance the blank-node counter past an attached bundle's _:bN labels in DocumentBuilder::addBundle(), so a later blank() cannot collide with them after flatten().
• Emit anonymous records in PROV-JSONLD through a shared BlankLabelMinter (also used by the JSON serializer), which previously dropped them from the graph.
• Detect the QName datatype by resolved URI so a document binding a non-standard prefix to the XSD namespace (xs:QName) is recognized in JSON and XML, keeping a literal fast path for the standard spellings.
• Reject a negative ProvNSerializer indentation with a clear message rather than a raw str_repeat error.