Fix/fix anthropic payload handler

[cosminacho]

Problem

A regression was introduced in the thinking_enabled detection logic inside
BedrockInvokePayloadHandler and BedrockConversePayloadHandler. The original
code used a chained .get() with an or {} fallback:

thinking_enabled = (
    getattr(self.model, "model_kwargs", {}).get("thinking", {}).get("type")
    == "enabled"
)

The or {} fallback only fires for falsy values (None, False, 0,
{}). If the thinking key is present but holds a non-None, non-dict truthy
value — e.g. a plain string "enabled", a list, or an integer — the fallback
is skipped and .get("type") is called on a type that doesn't support it,
raising an AttributeError at inference time.

This manifested as a runtime crash for Anthropic models on Bedrock where the
thinking field was set to an unexpected shape.

Fix
Replace the or {} chain with an explicit isinstance guard:

_thinking = (getattr(self.model, "model_kwargs", None) or {}).get("thinking")
thinking_enabled = isinstance(_thinking, dict) and _thinking.get("type") == "enabled"

[ionut-mihalache-uipath]

not the best readable code, but it works