Support non-UTF-8 encoded iCalendar files

[SashankBhamidi]

iCalendar files are supposed to be UTF-8, but files from older clients (Lotus Notes, old Outlook) show up in Latin-1, Windows-1252, or with no declared encoding. Right now these fail with a UnicodeDecodeError before anonymization even starts.

Implementation

src/icalendar_anonymizer/io.py (or wherever file reading currently lives): try UTF-8 first, then fall back to chardet detection, then to Latin-1 as a last resort. Log what encoding was detected.

def read_calendar_file(path) -> str:
    raw = Path(path).read_bytes()
    try:
        return raw.decode("utf-8")
    except UnicodeDecodeError:
        detected = chardet.detect(raw)
        encoding = detected.get("encoding") or "latin-1"
        return raw.decode(encoding, errors="replace")

Add chardet as an optional dep. If not installed, fall back to Latin-1 directly with a warning.

Output is always UTF-8.

• Test with a Latin-1 encoded file from a real client
• Test with Windows-1252
• Test that output is always valid UTF-8
• CLI: add --encoding flag to force a specific encoding