Fix pydantic serialization of tzinfo objects in DatetimeRangeWithTZColumn

[Copilot]

CI was failing with PydanticSerializationError: Unable to serialize unknown type when serializing DatetimeRangeWithTZColumn models containing tzinfo objects in the time_zones field.

Changes

• Add field_serializer for time_zones: Converts tzinfo objects to string names via get_tzname() during pydantic serialization
• Fix error message construction: Convert tuple concatenation to f-string in check_duplicated_time_zones validator
• Fix hardcoded column name: Use self.time_zone_column instead of literal "time_zone" in TimeZoneConverterByColumn.generate_to_schema()
• Improve documentation: Replace TODO comments with explanatory comments for get_time_zones() methods that return empty lists
• Fix typos: Correct 'eactual' → 'actual', 'srd_schema' → 'src_schema', 'will aligned' → 'will be aligned'

Example

from chronify.time_configs import DatetimeRangeWithTZColumn
from zoneinfo import ZoneInfo

config = DatetimeRangeWithTZColumn(
    start=datetime(2020, 1, 1),
    resolution=timedelta(hours=1),
    length=24,
    time_zone_column="tz",
    time_zones=[ZoneInfo("US/Eastern"), None]
)

# Now serializes correctly to:
# {"time_zones": ["US/Eastern", "None"], ...}
config.model_dump()

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