Modernize Compel for Transformers 5 and add diffusers smoke coverage

[lstein]

Applies upstream PR damian0815/compel#129 ("Modernize Compel for Transformers 5 and add diffusers smoke coverage") to this fork.

Changes

• Raise support floor to Python >=3.10; align CI matrix (drop 3.9)
• Update transformers guidance to >=5,<6; pin pyparsing~=3.0
• Migrate deprecated pyparsing API (delimited_list → DelimitedList)
• Remove stray networkx import in convenience_wrappers.py
• Add public-API / CLIP / SD / SDXL / T5 smoke tests and diffusers prompt_embeds / pooled_prompt_embeds coverage (incl. opt-in local SDXL single-file checkpoint tests gated behind COMPEL_RUN_LOCAL_CHECKPOINT_TESTS=1)
• Add provider tests for pooled output handling and BOS-less T5 behavior
• README cleanup and example typo fixes (negative_prompt_embed → negative_prompt_embeds)

Validation

• Created a fresh venv (Python 3.12.3), editable install pulled transformers 5.9.0, diffusers 0.38.0, pyparsing 3.3.2
• PYTHONPATH=src:test python -m unittest discover -s test → 61 passed, 1 skipped (the opt-in local checkpoint test)

⚠️ Note for reviewers

This raises the dependency floor to transformers >=5,<6. Please confirm compatibility with InvokeAI's own transformers pins before merging into main.

🤖 Generated with Claude Code