feat: enhance text protocol conversion and advanced custom routing (#5825)

* refactor: consolidate relay protocol converters

* refactor relayconvert text converters

* feat: refine relay converters and advanced custom routing

* refactor: enhance logging and add thought signature handling for Gemini requests

* refactor: enhance channel cache and pricing endpoint handling for advanced custom models

* feat: preserve billing usage semantics

* feat: add protocol-aware billing usage

* Delete useless files

* chore: update action versions in workflow files

* chore: update Docker action versions in workflow files

* fix: harden billing usage settlement and hot-path route matching

- estimate Gemini completion tokens locally when billable usageMetadata is
  prompt-only but output content was received (e.g. client aborts the stream
  before the final chunk), and rebuild the attached billing_usage as estimated
  so settlement does not bill zero output tokens
- guard NewClaudeMessagesBillingUsage against all-zero ClaudeUsage, matching
  the OpenAI/Gemini constructors, so a zero billing_usage cannot override a
  non-zero top-level usage during settlement
- cache compiled advanced-custom route model regexes; they run on the request
  hot path and were recompiled per request
- move the effectiveBillingUsage remap to PostTextConsumeQuota only, and
  document that calculateTextQuotaSummary expects remapped usage
- document the updatePricingLock -> channelSyncLock lock ordering that
  InitChannelCache/CacheUpdateChannel rely on, and the aux-struct pitfall in
  GeminiChatResponse.UnmarshalJSON

service/relayconvert/internal/jsonutil/stringify.go

@@ -0,0 +1,15 @@
+package jsonutil
+
+import (
+	"fmt"
+
+	"github.com/QuantumNous/new-api/common"
+)
+
+func ToJSONString(v interface{}) string {
+	bytes, err := common.Marshal(v)
+	if err != nil {
+		return fmt.Sprintf("%v", v)
+	}
+	return string(bytes)
+}