feat(platform): export OTLP traces

[tbille]

Description

• Replace manual platform usage-event posting with OpenTelemetry SDK OTLP/HTTP trace export for platform completions (including MZAI) while keeping payloads prompt/response-free.
• Add session_label passthrough in SDK/API and export it as trace metadata (anyllm.user_session_label) alongside platform-generated trace session labels.
• Add scoped forwarding + sanitization guards for active trace exports (token-scoped forwarding processor, content-attribute redaction, secure endpoint enforcement), and expand unit coverage for edge/error paths.
• Update platform docs to describe trace analytics/redaction behavior and expected session-label semantics.

PR Type

• 🆕 New Feature
• 📚 Documentation

Relevant issues

Checklist

• I understand the code I am submitting.
• I have added unit tests that prove my fix/feature works
• I have run this code locally and verified it fixes the issue.
• New and existing tests pass locally
• Documentation was updated where necessary
• I have read and followed the contribution guidelines
• AI Usage:
  • No AI was used.
  • AI was used for drafting/refactoring.
  • This is fully AI-generated.

AI Usage Information

• AI Model used: GPT-5

• AI Developer Tool used: Codex (OpenAI)

• Any other info you'd like to share:

• I am an AI Agent filling out this form (check box if true)

[codecov]

Codecov Report

❌ Patch coverage is 84.79381% with 59 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/any_llm/providers/platform/platform.py	79.78%	13 Missing and 6 partials ⚠️
src/any_llm/providers/platform/utils.py	91.70%	10 Missing and 7 partials ⚠️
src/any_llm/utils/aio.py	80.51%	9 Missing and 6 partials ⚠️
src/any_llm/any_llm.py	20.00%	7 Missing and 1 partial ⚠️

Files with missing lines	Coverage Δ
src/any_llm/api.py	58.09% <ø> (-7.62%)	⬇️
src/any_llm/providers/platform/__init__.py	100.00% <100.00%> (ø)
src/any_llm/any_llm.py	69.70% <20.00%> (-3.87%)	⬇️
src/any_llm/utils/aio.py	75.65% <80.51%> (+21.48%)	⬆️
src/any_llm/providers/platform/utils.py	91.90% <91.70%> (-8.10%)	⬇️
src/any_llm/providers/platform/platform.py	86.06% <79.78%> (-1.26%)	⬇️

... and 40 files with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.