feat(crewai): support tracing crewAI flows (#14082)

[MLOB-2806]

This PR adds support for APM and LLMObs tracing of CrewAI flows,
including the overall flow execution and individual start/listener
method execution, as well as span linking of which methods triggered
other methods in the flow (includes support for linking conditional
AND/OR and router method triggers).

(Due to some type hinting issues, I've removed `CrewAIIntegration`
import from `llmobs/_integrations/__init__.py`. Python 3.8 has issues
with subscripting WeakKeyDictionary, but CrewAI (and also LangGraph)
only run on Python 3.9/3.10+ so we didn't know this was an issue until
now)

Note (assist for reading test assertions): span linking/event tests in
`test_crewai_llmobs.py` are based on a complex flow that looks like
this:
<img width="974" height="627" alt="Screenshot 2025-07-30 at 4 23 59 PM"
src="https://github.com/user-attachments/assets/c784fe1b-6574-4735-a632-ec63a245ffc9"
/>

Additional note: tested
[manually](https://dd.datad0g.com/llm/traces?query=%40ml_app%3Aml-app%20%40event_type%3Aspan%20%40parent_id%3Aundefined&agg_m=count&agg_m_source=base&agg_t=count&fromUser=false&llmPanels=%5B%7B%22t%22%3A%22sampleDetailPanel%22%2C%22rEID%22%3A%22AwAAAZhc-Jpa5Z3YfgAAABhBWmhjLUpwYUFBRHBkZlpaLTBvekFBQUEAAAAkMDE5ODVjZjktYTNkYS00ZGEzLWE3NGYtOTQ1NmI4YWU2Mjg1AAAAfQ%22%7D%5D&spanId=14559885504901134809&start=1753820708729&end=1753907108729&paused=false)
and verified that crews are compatible with being run inside flows (as
is a documented use case in CrewAI):
<img width="707" height="685" alt="Screenshot 2025-07-30 at 4 25 48 PM"
src="https://github.com/user-attachments/assets/cc694c63-e043-4d36-a58d-5d65b31616cc"
/>

## Checklist
- [x] PR author has checked that all the criteria below are met
- The PR description includes an overview of the change
- The PR description articulates the motivation for the change
- The change includes tests OR the PR description describes a testing
strategy
- The PR description notes risks associated with the change, if any
- Newly-added code is easy to change
- The change follows the [library release note
guidelines](https://ddtrace.readthedocs.io/en/stable/releasenotes.html)
- The change includes or references documentation updates if necessary
- Backport labels are set (if
[applicable](https://ddtrace.readthedocs.io/en/latest/contributing.html#backporting))

## Reviewer Checklist
- [x] Reviewer has checked that all the criteria below are met 
- Title is accurate
- All changes are related to the pull request's stated goal
- Avoids breaking
[API](https://ddtrace.readthedocs.io/en/stable/versioning.html#interfaces)
changes
- Testing strategy adequately addresses listed risks
- Newly-added code is easy to change
- Release note makes sense to a user of the library
- If necessary, author has acknowledged and discussed the performance
implications of this PR as reported in the benchmarks PR comment
- Backport labels are set in a manner that is consistent with the
[release branch maintenance
policy](https://ddtrace.readthedocs.io/en/latest/contributing.html#backporting)


[MLOB-2806]:
https://datadoghq.atlassian.net/browse/MLOB-2806?atlOrigin=eyJpIjoiNWRkNTljNzYxNjVmNDY3MDlhMDU5Y2ZhYzA5YTRkZjUiLCJwIjoiZ2l0aHViLWNvbS1KU1cifQ

Author: Yun-Kim

.riot/requirements/181e571.txt

@@ -0,0 +1,160 @@
+#
+# This file is autogenerated by pip-compile with Python 3.11
+# by the following command:
+#
+#    pip-compile --allow-unsafe --no-annotate --resolver=backtracking .riot/requirements/1ce4995.in
+#
+aiohappyeyeballs==2.6.1
+aiohttp==3.12.15
+aiosignal==1.4.0
+annotated-types==0.7.0
+anyio==4.10.0
+appdirs==1.4.4
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+chromadb==1.0.16
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+coloredlogs==15.0.1
+coverage[toml]==7.10.3
+crewai==0.157.0
+cryptography==45.0.6
+decorator==5.2.1
+diskcache==5.6.3
+distro==1.9.0
+docstring-parser==0.17.0
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+openpyxl==3.1.5
+opentelemetry-api==1.36.0
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+opentelemetry-semantic-conventions==0.57b0
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+packaging==25.0
+parso==0.8.4
+pdfminer-six==20250506
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+pytest-asyncio==1.1.0
+pytest-cov==6.2.1
+pytest-mock==3.14.1
+python-dateutil==2.9.0.post0
+python-dotenv==1.1.1
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+pyyaml==6.0.2
+referencing==0.36.2
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+zipp==3.23.0