fix(anthropic): tool result caching

[sixlive]

Description

Refactor of #485.

Problem

When using tool_result_cache_type in multi-step tool calling scenarios, cache_control was being applied to every ToolResultMessage instead of just the last one. This could exceed Anthropic's 4 cache breakpoint limit and is unnecessary since the system uses "longest matching prefix" caching.

Solution

Move cache control application from Text.php (per-message during handleToolCalls()) to MessageMap::map() where it applies cache_control only to the last ToolResultMessage across all messages.

Changes

• Text.php: Remove automatic cacheType application to each ToolResultMessage
• MessageMap.php: Apply cache_control only to the last tool result message
• ToolResultCachingTest.php: Unit and integration tests for the fix
• Fixtures: Real API response fixtures for integration testing