Support for non-UTC time zones in datetime conversion

[wtn]

Fixes #130.

_to_ruby_datetime raised Todo for non-UTC zones, and datetime_to_rb_object .unwrap()'d the funcall, so the Ruby exception became a thread panic.

Moves datetime conversion into Rust, mirroring py-polars (crates/polars-python/src/conversion/datetime.rs): chrono-tz for named zones, FixedOffset for offsets. any_value_into_rb_object now returns RbResult<Value> so tz parse errors raise instead of panic. Ruby-side _to_ruby_datetime is removed.

[ankane]

Hi @wtn, thanks for the PR. Looks good overall, but a few comments:

1. Please mirror the code exactly when possible, including the style (there are minor differences in chunked_array.rs and larger differences in datetime.rs)
2. It looks like Python still calls to_py_datetime when year >= 2100, so I'm not sure _to_ruby_datetime should be removed
3. Please use Assisted-by: instead of Co-authored-by: for Claude, like Linux

[wtn]

Thank you for feedback.

I've updated the commit message trailer, revised chunked_array.rs and datetime.rs, and restored _to_ruby_datetime with the addition of TZInfo for year >= 2100.

[ankane]

Thanks, added some comments inline.

[ankane]

Looks great, thanks!

[ankane]

Made tzinfo optional in 6e775f1.

[wtn]

Thank you!