[FEATURE] Deprecate cache_tools option in BedrockModel

[minorun365]

Problem Statement

Currently, BedrockModel has two cache-related options with inconsistent deprecation status:

• cache_prompt - already deprecated (warns to use SystemContentBlock with cachePoint)
• cache_tools - not yet deprecated (no warning)

With the introduction of CacheConfig(strategy="auto") in PR #1438, there's now a cleaner way to handle prompt caching. However, the cache_tools option remains without a clear migration path or deprecation warning.

This inconsistency may confuse users about which options are recommended.

Proposed Solution

Add a deprecation warning for cache_tools similar to cache_prompt:

if self.config.get("cache_tools"):
    warnings.warn(
        "cache_tools is deprecated. Use <recommended_alternative> instead.",
        UserWarning, stacklevel=3
    )

Questions before implementation:

1. Should cache_tools be deprecated?
2. What is the recommended alternative?
   • Does CacheConfig(strategy="auto") cover tool caching use cases?
   • Or should users use cachePoint in the tools list directly?

Use Case

When users configure BedrockModel with both cache_prompt and cache_tools, only cache_prompt shows a deprecation warning. This creates confusion about whether cache_tools is still a recommended option.

model = BedrockModel(
    model_id="us.anthropic.claude-sonnet-4-5-20250929-v1:0",
    cache_prompt="default",  # ⚠️ Warning shown
    cache_tools="default",   # No warning - is this still OK to use?
)

Consistent deprecation messaging would help users migrate to the recommended approach.

Alternatives Solutions

1. Keep cache_tools as-is - If there's no suitable alternative yet, document that cache_tools is the only way to cache tool definitions.

2. Extend CacheConfig to support tools - Add a cache_tools strategy option to CacheConfig for unified caching configuration.

Additional Context

• Related: feat(bedrock): add automatic prompt caching support #1438 (automatic prompt caching with CacheConfig)
• Related: [FEATURE] Prompt caching support for all models #1140 (prompt caching support for all models)
• Related: [FEATURE] cache_messages argument for Bedrock model provider #404 (cache_messages feature request)
• Related: [FEATURE] Amazon Nova tool caching with cachePoint in messages #449 (Amazon Nova tool caching)

I have a draft implementation ready and can submit a PR once the migration path is clarified.