[docs] LTX-2.5 Modular Pipeline Docs (#14450)

* LTX-2.5 modular pipeline init docs

* Update LTX-2.5 modular docs now that the modular pipeline automatic downloads the Gemma 4 prompt enhancer and processor

* fix some modular docs typos

* fix more typos

* Update docs/source/en/api/pipelines/ltx2.md

Co-authored-by: Steven Liu <59462357+stevhliu@users.noreply.github.com>

* Remove unused transformers imports from LTX-2.5 modular examples

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Co-authored-by: Steven Liu <59462357+stevhliu@users.noreply.github.com>