refactor: LangChain LLM event refactor

[amychisholm03]

Description

Refactors LangChain LLM events. Introduces the base LlmTool class. I forgot to include LlmTool.agent_name in the initial LlmTool class, so that's included now too.

There are some fields that are not present in the AIM spec (appName, metadata tags) but were mentioned in the initial CDD for LangChain instrumentation, so I kept them.

How to Test

npm run unit
npm run versioned langchain
npm run versioned langchain-openai
npm run versioned langchain-aws

Related Issues

Part of #3687

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.51%. Comparing base (0ccad21) to head (0f64641).
⚠️ Report is 2 commits behind head on main.

❗ There is a different number of reports uploaded between BASE (0ccad21) and HEAD (0f64641). Click for more details.

HEAD has 2 uploads less than BASE

Flag	BASE (0ccad21)	HEAD (0f64641)
integration-tests-cjs-20.x	1	0
integration-tests-cjs-24.x	1	0

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3745      +/-   ##
==========================================
- Coverage   90.11%   81.51%   -8.60%     
==========================================
  Files         449      440       -9     
  Lines       58495    57166    -1329     
  Branches        1        1              
==========================================
- Hits        52710    46598    -6112     
- Misses       5785    10568    +4783     

Flag	Coverage Δ
integration-tests-cjs-20.x	?
integration-tests-cjs-24.x	?
integration-tests-esm-20.x	52.98% <55.18%> (+0.02%)	⬆️
integration-tests-esm-24.x	54.20% <65.14%> (+0.03%)	⬆️
versioned-tests-20.x	81.39% <100.00%> (-0.29%)	⬇️
versioned-tests-22.x	81.40% <100.00%> (-0.29%)	⬇️
versioned-tests-24.x	81.31% <100.00%> (-0.28%)	⬇️

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[jsumners-nr]

Please consider incorporating amychisholm03#14