feat: support claude cache and thinking for upstream [OpenRouter] (#983)

* feat: support claude cache for upstream [OpenRouter]

* feat: support claude thinking for upstream [OpenRouter]

* feat: reasoning is common params for OpenRouter

relay/channel/openrouter/dto.go

@@ -0,0 +1,9 @@
+package openrouter
+
+type RequestReasoning struct {
+	// One of the following (not both):
+	Effort    string `json:"effort,omitempty"`     // Can be "high", "medium", or "low" (OpenAI-style)
+	MaxTokens int    `json:"max_tokens,omitempty"` // Specific token limit (Anthropic-style)
+	// Optional: Default is false. All models support this.
+	Exclude bool `json:"exclude,omitempty"` // Set to true to exclude reasoning tokens from response
+}