JSCalendar and jCal anonymization support

[SashankBhamidi]

The anonymizer handles iCalendar (.ics) files. JSCalendar (RFC 8984) and jCal (RFC 7265) are now common enough that missing support is a real gap.

src/icalendar_anonymizer/formats/jscal.py for JSCalendar (JSON), src/icalendar_anonymizer/formats/jcal.py for jCal (JSON array format).

Both formats carry the same personal data as iCalendar: summaries, descriptions, attendee emails, organizer info, locations, URLs. The anonymization logic is the same. The format-specific code is just parse-transform-serialize.

JSCalendar support depends on calendaring-jmap being available for parsing. Add it as an optional dep:

[project.optional-dependencies]
jscal = ["calendaring-jmap>=1.0"]

jCal is a JSON representation of iCalendar and can be parsed without calendaring-jmap.

• anonymize_jscal(data: dict) -> dict
• anonymize_jcal(data: list) -> list
• CLI: auto-detect format from file extension (.json with JSCalendar root key vs jCal array)
• Tests for both formats with real-world samples
• Docs: add JSCalendar and jCal to the supported formats section