👌 Add ability to localize figure caption

[j123b567]

Sphinx localization needs node source and line and if it is not present, localization step is skipped.

If the source looks like (MyST markdown)

::::{subfigure} A

:::{image} img1.png
:alt: Subfigure caption
:width: 100px
:::

Figure caption
::::

Then after running make gettext, this .pot file is generated

#: ../../index.md:1
msgid "Subfigure caption"
msgstr ""

After applying the PR, this .pot file is generated

#: ../../index.md:1
msgid "Subfigure caption"
msgstr ""

#: ../../index.md:8
msgid "Figure caption"
msgstr ""

[codecov-commenter]

Codecov Report

Attention: 4 lines in your changes are missing coverage. Please review.

Comparison is base (fb52892) 80.65% compared to head (c79156f) 79.78%.

Files	Patch %	Lines
src/sphinx_subfigure/main.py	0.00%	4 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##             main      #14      +/-   ##
==========================================
- Coverage   80.65%   79.78%   -0.88%     
==========================================
  Files           5        5              
  Lines         274      277       +3     
==========================================
  Hits          221      221              
- Misses         53       56       +3     

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[chrisjsewell]

looks good thanks!