Fix Dependencies & Imports

[aryasoni98]

Context:
Some modules (a2a, opentelemetry, openinference) are either missing or incorrectly imported, which blocks new contributors from running the SDK.

Tasks:

• Verify all imports resolve correctly
• Update requirements.txt / pyproject.toml
• Add installation notes to README.md

Impact:
Makes the SDK immediately usable → smoother onboarding and first contribution.

[g3force]

Can't reproduce. Check workflow runs fine.