Fix table markup alignment

[avehtari]

Fix table column alignment with bold/italic markup

When markdown-hide-markup is enabled, bold and italic delimiters (**, *) are
hidden from display but markdown-table-align pads cells based on raw character
width including those delimiters. This causes columns with markup to appear narrower
than intended:

• Bold cell (**text**): 4 chars too narrow
• Italic cell (*text*): 2 chars too narrow

Example

| **Column A** | **Column B** |        | Column A | Column B |
|--------------|--------------|   →    |----------|----------|
| **25**       | 30           |        | 25   | 30           |
| 40           | *50*         |        | 40       | 50       |
  raw text (aligned)                     displayed (misaligned)

Fix

After markdown-table-align pads each table, a new function
eca-table--compensate-hidden-markup scans each cell for */** delimiter
pairs via regex and adds an overlay with an after-string of compensating
spaces:

| Column A     | Column B     |
|--------------|--------------|
| 25    ····   | 30           |   (···· = 4-space overlay after-string)
| 40           | 50  ··       |   (·· = 2-space overlay after-string)

Key details:

• Regex-based counting — does not depend on font-lock timing
• Overlay-only — no buffer text modification; overlays use eca-table-markup-pad
  property (not eca-table-overlay) so eca-table-remove-overlays in the beautify
  step does not wipe them
• Idempotent — removes previous compensation overlays before reapplying
• 1-char overlay — avoids zero-width overlays which Emacs deletes immediately
  when evaporate is set
• eca-table--max-line-width updated to subtract hidden markup for accurate
  wide-table detection

Files changed

• eca-table.el — added eca-table--count-markup-chars,
  eca-table--compensate-hidden-markup; updated eca-table-align and
  eca-table--max-line-width
• test/eca-table-markup-test.el — interactive visual test (M-x eca-table-markup-test)

Notes

Code and PR description with help from Claude. In addition to the test code included, I have tested with many other tables.
and programmatic checks (M-x eca-table-markup-test-run-checks)

[ericdallo]

Thank you!