docs: fix stale table.direction example to table_direction in WD_TABLE_DIRECTION

[MohammadaliMasjedi-source]

What's wrong

The documented example for WD_TABLE_DIRECTION shows:

from docx.enum.table import WD_TABLE_DIRECTION

table = document.add_table(3, 3)
table.direction = WD_TABLE_DIRECTION.RTL

But the Table object exposes the property as table_direction, not direction. Because
Table has no __slots__, table.direction = WD_TABLE_DIRECTION.RTL does not raise — it
just creates a throwaway instance attribute that nothing ever reads and that never writes
<w:bidiVisual>. So the documented example is a silent no-op: the user gets no signal that
RTL was never applied, which is arguably worse than an error.

The stale example appears in two places:

1. src/docx/enum/table.py — docstring of class WD_TABLE_DIRECTION
2. docs/api/enum/WdTableDirection.rst — the rendered API-reference page

What this PR changes

Replace table.direction with table.table_direction in both spots, so the documented example
actually applies right-to-left cell ordering. Docs only — no code/behavior change.

This also clears up the confusion behind #1502: RTL cell ordering is supported —
table.table_direction = WD_TABLE_DIRECTION.RTL writes <w:bidiVisual/> into w:tblPr. The
mechanism existed; the docs example was just mis-named.

How I verified it

Ran a small script against python-docx==1.2.0 (current latest, matching master):

1. table.direction = ... does not raise, but also does not write <w:bidiVisual> (silent no-op);
2. table.table_direction = WD_TABLE_DIRECTION.RTL sets and round-trips correctly;
3. only the table_direction assignment makes the saved document's w:tblPr contain <w:bidiVisual>.

All checks passed.

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I put this together with some AI assistance for the drafting, and verified the behavior against
master myself with a small script before opening the PR. Happy to adjust to your preferences.