chore(core): add ruff rule PLR2004

[cbornet]

No description provided.

[codspeed-hq]

CodSpeed Performance Report

Merging #33706 will not alter performance

_{Comparing cbornet:core-plr2004 (dfb5904) with master (d1e2099)}

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Summary

✅ 13 untouched
⏩ 21 skipped¹

Footnotes

1. 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. ↩

[Copilot]

Pull Request Overview

This PR removes the ruff linting rule PLR2004 (comparison to magic numbers) from the global ignore list and replaces hardcoded numeric literals throughout the codebase with named constants to improve code readability and maintainability.

• Extracted magic numbers into descriptive named constants across multiple files
• Improved error handling for tuple unpacking operations with better exception chaining
• Hardcoded Pydantic version flags to v2 only
• Fixed minor issues in error message formatting and conditional logic

Reviewed Changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
libs/core/pyproject.toml	Enabled PLR2004 rule globally, kept disabled for tests
libs/core/langchain_core/utils/pydantic.py	Hardcoded Pydantic version flags to v2 values
libs/core/langchain_core/utils/function_calling.py	Replaced magic number 2 with named constant _MIN_DOCSTRING_BLOCKS
libs/core/langchain_core/tools/base.py	Improved tuple unpacking error handling and updated error message
libs/core/langchain_core/runnables/graph_mermaid.py	Replaced magic number 500 with requests.codes.internal_server_error
libs/core/langchain_core/runnables/branch.py	Replaced magic number 2 with named constant _MIN_BRANCHES
libs/core/langchain_core/runnables/base.py	Replaced multiple magic numbers with named constants
libs/core/langchain_core/prompts/chat.py	Improved tuple unpacking validation with better error handling
libs/core/langchain_core/messages/utils.py	Improved tuple unpacking with try-except pattern
libs/core/langchain_core/language_models/chat_models.py	Replaced magic number 100 with named constant _MAX_CLEANUP_DEPTH