Add formatting attribute to support more bibliography styles

[pluto-han]

Hi @michel-kraemer, I am a GSoC student in @JabRef working on my project Improved LibreOffice-JabRef integration.

Thank you very much for your work!

Follow up #338
Refs JabRef/jabref#16555 (comment)

Issue

Formatting attributes on cs:date and cs:date-part elements are currently not preserved in rendered output.

For example, Advanced Functional Materials marks a date as bold:

<date variable="issued" font-weight="bold">
  <date-part name="year"/>
</date>

But citeproc-java produces the following HTML output:

<div class="csl-entry">
  <div class="csl-left-margin">[1] </div><div class="csl-right-inline">M. Macht, J. Mueller, <span style="font-style: italic">Appetite</span> 2007, <span style="font-style: italic">49</span>, 667.</div>
</div>

Rendered output:
[1] M. Macht, J. Mueller, Appetite 2007, 49, 667.
As seen in JabRef -

Expected:
[1] M. Macht, J. Mueller, Appetite 2007, 49, 667.
As seen in Zotero -

(The following part was generated by gpt 5.5 and reviewed & edited by me)

Cause/Analysis

SDate and SDatePart parse affixes and other date-specific behavior, but they do not read or apply FormattingAttributes.

This means formatting attributes such as font-weight, font-style, vertical-align, etc. are ignored when they are placed directly on cs:date or cs:date-part.

Fix

This change adds FormattingAttributes support to both date rendering classes:

• SDate now reads formatting attributes from the cs:date node and emits the rendered date content with those attributes.
• SDatePart now reads formatting attributes from the cs:date-part node and emits the rendered date part value with those attributes.

Affix handling remains unchanged, so this does not widen the special cs:layout affix behavior fixed in #338 to other rendering elements.

Tests

Added a regression test covering both cases:

• formatting attributes on cs:date
• formatting attributes on cs:date-part

The test verifies that HTML output preserves the expected formatting, e.g.:

<span style="font-weight: bold">2007</span>

I ran:

JAVA_HOME=$(/usr/libexec/java_home -v 17) ./gradlew :citeproc-java:test

and all tests pass.

[pluto-han]

cc @subhramit @Siedlerchr