0.17.3 MathTable - first and last column of MathTable are truncated

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## Description of bug / unexpected behavior
Setting a fixed width of the columns in a MathTable() is not correctly supported for the first and last column, which are truncated at the left and right edge of the table elements.

## Expected behavior
The given width should be obeyed independent on the contents of the cells.

## How to reproduce the issue
Code for reproducing the problem

```python
class Test(Scene):
def construct(self):
mytable = MathTable(
[[1, 10, 100, 1000, 10000, 100000], [0,0,0,0,0,0]],
h_buff=.1,
v_buff=.1,
include_outer_lines=True,
arrange_in_grid_config={"col_widths":[3]*6, "col_alignments": ["c"]*6}
).scale_to_fit_width(10)
self.add(mytable)
```

## Additional media files
Images/GIFs

## System specifications

System Details

- OS: Windows 10 64bit
- Python version (`python/py/python3 --version`): 3.11.6

LaTeX details
+ LaTeX distribution (e.g. TeX Live 2020): MikTex

Start with the MathTable entry point and reproduce the supplied Scene using arrange_in_grid_config and scale_to_fit_width. Trace how the outer columns are laid out and rendered, then verify that the fixed widths remain visible at both table edges regardless of cell contents. Add regression coverage for the reported example if the relevant test location is identified.

Written by the indexing model from the issue text.