refactor: Updated @langchain/core instrumentation to subscribe to events emitted

[amychisholm03]

This PR resolves #3442.

[codecov]

Codecov Report

❌ Patch coverage is 96.84466% with 26 lines in your changes missing coverage. Please review.
✅ Project coverage is 97.64%. Comparing base (37c43f5) to head (a050bbb).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
lib/subscribers/langchain/runnable.js	89.28%	6 Missing ⚠️
lib/subscribers/langchain/tool.js	93.18%	6 Missing ⚠️
lib/subscribers/langchain/vectorstore.js	95.48%	6 Missing ⚠️
lib/subscribers/base.js	44.44%	5 Missing ⚠️
lib/subscribers/langchain/runnable-stream.js	97.81%	3 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #3493       +/-   ##
===========================================
+ Coverage   81.46%   97.64%   +16.17%     
===========================================
  Files         409      422       +13     
  Lines       54383    55857     +1474     
  Branches        1        1               
===========================================
+ Hits        44305    54539    +10234     
+ Misses      10078     1318     -8760     

Flag	Coverage Δ
integration-tests-cjs-20.x	74.03% <50.60%> (?)
integration-tests-cjs-22.x	74.07% <50.60%> (?)
integration-tests-cjs-24.x	74.83% <50.60%> (?)
integration-tests-esm-20.x	52.70% <50.60%> (+0.20%)	⬆️
integration-tests-esm-22.x	52.75% <50.60%> (+0.20%)	⬆️
integration-tests-esm-24.x	53.95% <50.60%> (+0.19%)	⬆️
unit-tests-20.x	88.71% <50.60%> (?)
unit-tests-22.x	88.75% <50.60%> (?)
unit-tests-24.x	88.76% <50.60%> (?)
versioned-tests-20.x	81.08% <96.84%> (-0.25%)	⬇️
versioned-tests-22.x	81.08% <96.84%> (-0.25%)	⬇️
versioned-tests-24.x	81.02% <96.84%> (-0.24%)	⬇️

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[bizob2828]

Same as google gen ai. we need to look at the spec for enabling/disabling AI monitoring, not sure if we have this correct

[bizob2828]

this is not what you may think it is. This is to increment a tracking metric which doesn't apply here because we instrument these packages

[bizob2828]

Before this was technically broken. The package that currently gets registered is @langchain/core. So if a customer wants to disable langchain instrumentation they can set this.config.instrumentation['@langchain/core'].enabled to false. We will have to update angler to properly track this package though

[amychisholm03]

It will not create the Supportability metric if I omit this. Because @langchain/core itself is never required directly, I had to add its children packages here in order for the metrics to be created.

[bizob2828]

let's talk about this as well. this is not the place for this