feat(examples-py): add Helicone Manual Logger validation

[Nightingalelyy]

Summary

• Add a Python Helicone Manual Logger example set covering request helpers, builders, streaming, tool/vector/data events, Anthropic, chat completion, embeddings, privacy, delayed contexts, cancellation, nested failure, and expected-error paths.
• Include deterministic local sinks, a feature runner, contract tests, and setup documentation.
• Exercise the matching instrumentation from Python instrumentation PR #398.

Validation

• Example contract tests: 8 passed
• Ruff check and format validation
• Deterministic runner: 17/17 scenarios
• Respan platform validation: 17 traces, 35 span records, 18 instrumentation spans, no duplicates, and 43/43 semantic assertions