🔧 Deprecate the never-functional needtable style_col option

[chrisjsewell]

The option has never done anything

git grep -n style_col across the whole tree returns exactly five hits, every one a declaration or a dump of one:

• sphinx_needs/directives/needtable.py — the option_spec entry, the self.options.get, and the node-attribute assignment
• sphinx_needs/data.py — the NeedsTableType TypedDict field
• one style_col="" in a doctree snapshot

process_needtables never reads current_needtable["style_col"] back. There is no CSS and no JS keyed on it, and it is absent from docs/directives/needtable.rst, which documents every other option (including its functional sibling :style_row:). A build that sets it renders exactly as one that does not.

Shape: deprecate-and-warn, not remove (maintainer ruling)

The option stays in option_spec so existing documents keep building unchanged, and setting it now emits a deprecated warning stating the truth:

The 'style_col' option has never had any effect (it was collected but never applied) and will be removed; the line can be deleted.

This is the export_id pattern — an easy deprecation pathway instead of an unknown-option error. The dead plumbing is still removed (the TypedDict field, the node attribute, the collection), so nothing stores or transports the value anymore.

A test pins the warning firing exactly once (tests/doc_test/doc_needtable/test_styles.rst gained a table carrying the option), and the doctree snapshot loses its inert style_col="" attribute.

Also folded in: the show_parts docs example was rendering an empty table

The example needtable in docs/directives/needtable.rst's show_parts section filters on :tags: test_table — but none of the three needs its dropdown defines (table_001..table_003) carried that tag, so the rendered table selected nothing. The three needs are now tagged, and a scratch build confirms the intended output: each need's row, with table_001's three part rows directly beneath it and the part links resolved. (This example doubles as the manual cross-check for ubCode's :show_parts: implementation in useblocks/ubcode#2990.)

Found while implementing the needtable options in ubCode (useblocks/ubcode#2983 / useblocks/ubcode#2990): ubCode used to warn that :style_col: was "not yet applied", which wrongly implied a Sphinx-Needs build applies it — its warning now states the option has no effect in either tool.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.56%. Comparing base (4e10030) to head (ecb26ac).
⚠️ Report is 327 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1779      +/-   ##
==========================================
+ Coverage   86.87%   90.56%   +3.68%     
==========================================
  Files          56       76      +20     
  Lines        6532    11336    +4804     
==========================================
+ Hits         5675    10267    +4592     
- Misses        857     1069     +212     

Flag	Coverage Δ
pytests	90.56% <100.00%> (+3.68%)	⬆️

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