fix(aws): Update DeepSeek V3.x tool choice support on ChatBedrockConverse

[Michael Chin (michaelnchin)]

Fixes #1259

#688, merged in Oct. 2025, restricted DeepSeek V3 models to any ToolChoice mode (based on Bedrock V3.1's tested behavior and upstream V3.2-Exp's docs). However, since then, V3.1's tool choice behavior has changed, as well as that of the stable V3.2 version Bedrock added in Dec. 2025.

Manually ran tool_choice value tests against Converse API to confirm the current situation:

• With thinking disabled (model default), both DeepSeek V3.1 and V3.2 behave the same:
  • Both auto and any mode now work unconditionally
  • Specific tool mode, while still accepted by Converse API, is not obeyed by either model.
• With thinking enabled (via {"reasoning_effort": "high"}):
  • any doesn't produce tool calls on either V3.1 or V3.2
  • auto doesn't work on V3.1, but does on V3.2 (which matches the DeepSeek docs)
  • tool mode: same as non-thinking.

Based on these observations, updated the following for DeepSeek V3.1/3.2 on ChatBedrockConverse:

• Allowed ToolChoice values goes to ("auto", "any")
• Removed the forced any ToolChoice mode override for these models in bind_tools
• Added any -> auto auto-downgrade in the case that thinking is also enabled.
  • Note: may need further updates for when Bedrock adds DeepSeek V4, which now uses thinking by default; see: [BUG] DeepSeek V4 rejects tool_choice="required" and specific function tool_choice — breaks structured output in all agent frameworks deepseek-ai/DeepSeek-V3#1376