fix(anthropic): preserve message cache control for list content

[Oxygenesis]

Summary

• Preserve message-level cache_control for Anthropic list content by applying it to the last converted block when no block-level setting exists.
• Preserve the same behavior for Anthropic system/assistant paths and Bedrock Converse sync/async user paths.
• Keep block-level cache_control precedence.
• Add mocked regression coverage.

Problem

Fixes #43324. When content is a list, the translators inspect each content element but ignore cache_control on the containing message, so prompt-cache breakpoints disappear silently for Anthropic and Bedrock Converse.

Testing

• Targeted regression tests: 3 passed.
• Affected suites: 912 passed with the macOS text/markdown MIME mapping supplied; the native run otherwise hit one unrelated existing MIME-type fixture failure.
• Ruff format/check passed for the changed production modules.
• py_compile and git diff --check passed.
• No provider credentials or live model calls were used; the test socket guard blocked an attempted external connection.

[codspeed]

Merging this PR will not alter performance

✅ 31 untouched benchmarks

---

_{Comparing Oxygenesis:codex/anthropic-cache-control (ed55255) with main (d463049)}

[codecov]

Codecov Report

❌ Patch coverage is 96.96970% with 1 line in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...llm/litellm_core_utils/prompt_templates/factory.py	96.00%	1 Missing ⚠️

📢 Thoughts on this report? Let us know!

[Oxygenesis]

The latest head (ed55255) now passes the lint/type fix and coverage checks. The remaining misc shard is failing in four unrelated OpenAPI compliance tests: test_create_model_interaction_request_schema, test_input_types_match_spec, test_delete_endpoint_exists, and test_get_endpoint_exists in tests/unit/interactions/test_openapi_compliance.py (CreateModelInteractionParams and GET/DELETE interaction endpoints are absent from the loaded spec). This PR only changes Bedrock cache-control call typing and does not touch the interaction schema or tests, so I have left the unrelated baseline issue out of this PR.

[Oxygenesis]

Follow-up on the shared CI failure: the four OpenAPI failures in the misc shard are now isolated in #43807, which updates the compliance tests to the current live Interactions schema; its OpenAPI tests pass in CI. I'm keeping this Bedrock cache-control PR focused and leaving those unrelated test changes out. After #43807 lands, this PR should only need a misc-shard rerun.

[Oxygenesis]

I also opened #43812 for the separate ultrafast model-cost schema mismatch now present on main. This Bedrock cache-control PR remains unchanged; after the OpenAPI and cost-map maintenance fixes land, rerun the misc shard here.

[Oxygenesis]

Update: #43764 brought the ultrafast schema fields into main; #43807 now covers the remaining OpenAPI test drift, with refreshed CI running

[Oxygenesis]

Correction: #43532 now contains the current Interactions contract update and its misc shard passes; #43807 was a duplicate, so I closed it