fix(tracing): make OpenTelemetry an optional runtime dependency

[Yash1hi]

Problem

otel is declared as an optional extra in pyproject.toml, but import scorecard_ai failed entirely unless [otel] was installed:

ModuleNotFoundError: No module named 'opentelemetry'

The top-level package (src/scorecard_ai/__init__.py) eagerly imports lib/wrap_llms.py, which imported opentelemetry at module load time. So the documented pip install scorecard-ai produced a broken SDK — the otel extra was effectively mandatory just to use the core API client.

Reproduced (with opentelemetry absent):

>>> import scorecard_ai
ModuleNotFoundError: No module named 'opentelemetry'

Fix

Make OpenTelemetry genuinely optional by deferring its import to first use of the tracing wrappers:

• lib/_wrap_llms_otel.py (new) — the existing OpenTelemetry-backed implementation, moved verbatim. Still imports opentelemetry at the top.
• lib/wrap_llms.py — now a thin shim with no top-level otel import. wrap / wrap_openai / wrap_anthropic lazily import the implementation on first call. If opentelemetry is missing, they raise a clear ImportError pointing to pip install 'scorecard-ai[otel]' instead of breaking import of the whole SDK. The type-only WrapConfig stays under TYPE_CHECKING.

All three public import paths are preserved: scorecard_ai.wrap, scorecard_ai.lib.wrap, and scorecard_ai.lib.wrap_llms.wrap.

Verification

• ✅ import scorecard_ai succeeds with opentelemetry blocked; core Scorecard client constructs and works.
• ✅ wrap() without otel raises a helpful ImportError (not an opaque ModuleNotFoundError).
• ✅ With otel present, wrap() end-to-end still returns the _LLMClientWrapper; aliases preserved (wrap_openai is wrap).
• ✅ ruff check and ruff format pass on both files.

Notes

• Node SDK intentionally unchanged — @opentelemetry/* stay required dependencies there, so it already imports fine.
• The [otel] install for tracing is already documented in examples/README.md, and the new error message points there too.