Refactor langchain

[hmstepanek]

Overview

• Fix bug in vectorstore span names and add tests for span names
• Extract shared code into functions.
• Utilize attrs with value of None being dropped.
• Add tests for chain span names.
• Make sure the span is always exited before we record it's duration.

[github-actions[bot]]

🦙 MegaLinter status: ✅ SUCCESS

Descriptor	Linter	Files	Fixed	Errors	Elapsed time
✅ PYTHON	bandit	1		0	5.12s
✅ PYTHON	black	4	0	0	1.5s
✅ PYTHON	flake8	4		0	0.78s
✅ PYTHON	isort	4	0	0	0.3s
✅ PYTHON	pylint	4		0	6.26s

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[codecov-commenter]

Codecov Report

Attention: Patch coverage is 96.00000% with 6 lines in your changes are missing coverage. Please review.

Project coverage is 81.80%. Comparing base (b950070) to head (a3f56e4). Report is 20 commits behind head on develop-ai-limited-preview-3.

Files	Patch %	Lines
newrelic/hooks/mlmodel_langchain.py	96.00%	5 Missing and 1 partial :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop-ai-limited-preview-3 #1097 +/- ## ================================================================ - Coverage 81.86% 81.80% -0.06% ================================================================ Files 192 192 Lines 21253 21243 -10 Branches 3711 3692 -19 ================================================================ - Hits 17398 17378 -20 - Misses 2783 2793 +10 Partials 1072 1072 ```

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