Adding support for Polars structs (nushell#10943)

Provides support for reading Polars structs. This allows opening of
supported files (jsonl, parquet, etc) that contain rows with structured
data.

The following attached json lines
file([receipts.jsonl.gz](https://github.com/nushell/nushell/files/13311476/receipts.jsonl.gz))
contains a customer column with structured data. This json lines file
can now be loaded via `dfr open` and will render as follows:

<img width="525" alt="Screenshot 2023-11-09 at 10 09 18"
src="https://github.com/nushell/nushell/assets/56345/4b26ccdc-c230-43ae-a8d5-8af88a1b72de">


This also addresses some cleanup of date handling and utilizing
timezones where provided.

This pull request only addresses reading data from polars structs. I
will address converting nushell data to polars structs in a future
request as this change is large enough as it is.

---------

Co-authored-by: Jack Wright <jack.wright@disqo.com>

crates/nu-cmd-dataframe/Cargo.toml

@@ -19,6 +19,7 @@ nu-protocol = { path = "../nu-protocol", version = "0.86.1" }
 
 # Potential dependencies for extras
 chrono = { version = "0.4", features = ["std", "unstable-locales"], default-features = false }
+chrono-tz = "0.8"
 fancy-regex = "0.11"
 indexmap = { version = "2.1" }
 num = { version = "0.4", optional = true }