fix(docx): handle inline formulas in list items (#3304)

* fix(docx) Handle inline formulas in list items

Fixes issue where inline formulas in list items were ignored during conversion.
Added helper methods to eliminate code duplication.
Updated test data with list items containing inline equations.

Signed-off-by: Cesar Berrospi Ramis <ceb@zurich.ibm.com>

* fix(docx): collect element refs in _add_inline_equations_to_parent

Signed-off-by: Cesar Berrospi Ramis <ceb@zurich.ibm.com>

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Signed-off-by: Cesar Berrospi Ramis <ceb@zurich.ibm.com>