feat(core): enrich HTML pretty_repr for prompt templates and display partial variables

[antznette1]

• Enhances pretty_repr(html=True) for prompt templates to improve readability in notebooks/docs.
• Adds a consistent title via get_msg_title_repr.
• Displays partial_variables (colored when html=True).
• Applies to:
  • ChatPromptTemplate.pretty_repr
  • BaseStringMessagePromptTemplate.pretty_repr (shows partials from underlying prompt)
  • _StringImageMessagePromptTemplate.pretty_repr (aggregates partials across sub-prompts)

Lint and test

• Ran make format, make lint, and make test locally for the modified package.
• Added unit tests:
  • libs/core/tests/unit_tests/prompts/test_pretty_repr_chat.py
• New tests validate text and HTML output including partials for ChatPromptTemplate.

[codspeed-hq]

CodSpeed Performance Report

Merging #34073 will not alter performance

_{Comparing antznette1:feat/pretty-repr-html-partials (469d756) with master (880652b)¹}

⚠️ Unknown Walltime execution environment detected

Using the Walltime instrument on standard Hosted Runners will lead to inconsistent data.

For the most accurate results, we recommend using CodSpeed Macro Runners: bare-metal machines fine-tuned for performance measurement consistency.

Summary

✅ 13 untouched
⏩ 21 skipped²

Footnotes

1. No successful run was found on master (9c21f83) during the generation of this report, so 880652b was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

2. 21 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[antznette1]

@mdrxy @eyurtsev
Good day, hope everything is fine with you. Please, can you review my PR when you can?