fix(anthropic): emit prompt cache usage attributes

[jstar0]

Summary

• Extract Anthropic prompt-cache read and creation token counts from non-streaming messages and raw streaming metadata.
• Keep the existing prompt, completion, and total attributes based on Anthropic native input/output values.
• Cover synchronous and asynchronous stream final-message paths with fixture-based regressions.

Why

Anthropic reports cache-read and cache-creation tokens as fields separate from input_tokens. The instrumentation previously dropped those fields, making cache activity invisible to telemetry consumers. This change exposes both fields independently while preserving the existing native input/output total, so consumers can choose their accounting policy without double-counting cache tokens.

Validation

• uv run pytest -q tests/unit/instrumentation/anthropic/test_attributes.py tests/unit/instrumentation/anthropic/test_stream_wrapper.py — 22 passed
• uv run ruff check on the four changed files — passed
• uv run ruff format --check on the four changed files — passed

Fixes #1445