fix: `CellStyleBorders` is not properly constructed when `sides` is set to "all"

[jrycw]

It seems that the following code does not render as expected when sides is set to "all" for style.borders. The main reason might be the omission of other values while constructing a new CellStyleBorders.

import polars as pl
from great_tables import GT, md, html, style, loc
from great_tables.data import islands

islands_mini = (
    pl.from_pandas(islands).sort("size", descending=True)
    .head(10)
)

(
    GT(islands_mini)
    .tab_style(
      style=style.borders(sides=["all"], style="solid", weight="4px", color="red"),
      locations=loc.body(rows=[-1])
    )
)

The table comparison before and after fixing can be found as below:

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 83.43%. Comparing base (5ea06af) to head (368d05a).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #326 +/- ## ======================================= Coverage 83.43% 83.43% ======================================= Files 41 41 Lines 4287 4287 ======================================= Hits 3577 3577 Misses 710 710 ```

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[machow]

Ah, nice catch, thanks! I added a small lil test, and everything looks good!

[machow]

@rich-iannone do you mind merging? :)

[jrycw]

Ah, nice catch, thanks! I added a small lil test, and everything looks good!

@machow, thanks for adding a test.