Add optional OpenTelemetry tracing

[aakashH242]

Adds optional OpenTelemetry spans around sync and async trim, context, and batch operations, while keeping SDK configuration, exporters, resources, sampling, flushing, and shutdown under application control.

Span attributes are bounded and exclude input text, queries, wrappers, callback messages, and exception stack traces. Documentation covers no-op defaults and OTLP gRPC/HTTP setup. This release bumps the package to 0.7.0.

Validation:

• uv run pytest -m 'not integration' (281 passed, 1 deselected; 97.07% coverage)
• uv run ruff check . and uv run ruff format --check .
• uv run mypy src
• uv run mkdocs build --strict
• clean sdist/wheel build and fresh Python 3.12 wheel install smoke
• manual SDK sync, async, context, and batch span checks
• OTLP gRPC and HTTP export checks; Tempo readback verified scope, parentage, and attributes