[ES2-1256] convert es2 to pyenvector

[euphoria0-0]

langchain에서 SDK를 es2에서 pyenvector로 변환합니다

[Copilot]

Pull request overview

This PR migrates the SDK dependency from es2 to pyenvector, updating all references, imports, and documentation throughout the codebase. The change includes renaming environment variables, updating package dependencies, and refactoring code to use the new SDK's API.

Key changes:

• Updated package dependency from es2 to pyenvector in pyproject.toml and test requirements
• Renamed SDK references throughout the codebase (e.g., es2.ES2 → pyenvector.EnvectorClient)
• Updated environment variables from ES2_* to ENVECTOR_* prefix
• Added new methods similarity_search_with_score and similarity_search_with_score_by_vector to the vectorstore

Reviewed changes

Copilot reviewed 14 out of 15 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
pyproject.toml	Updated package version to 0.1.3, changed dependency from es2 to pyenvector, updated keywords
tests/requirements.txt	Updated wheel dependency from es2-1.0.3rc7 to pyenvector-1.2.0
tests/test_vectorstore.py	Added test coverage for new similarity_search_with_score methods
tests/integration/test_es2_integration.py	Updated environment variables and SDK imports to use pyenvector
pytest.ini	Updated marker description to reference EnVector instead of ES2
libs/envector/langchain_envector/client.py	Refactored to use pyenvector.EnvectorClient and pyenvector.Index
libs/envector/langchain_envector/vectorstore.py	Added new search methods and refactored to use shared internal method
libs/envector/langchain_envector/types.py	Updated comments to reference pyenvector
libs/envector/langchain_envector/init.py	Updated package docstring
libs/envector/examples/*.py	Updated requirement comments
libs/envector/README.md	Updated SDK references and added usage examples
README.md	Updated all SDK and environment variable references
CONTRIBUTE.md	Updated development guidelines and test instructions
.github/workflows/release.yaml	Updated release workflow to reference pyenvector

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