feat(usage): add support for requested model alias handling

- Introduced methods for setting and retrieving model aliases in execution and usage contexts.
- Enhanced `UsageReporter` and related structures to include client-requested aliases.
- Updated tests to validate alias propagation and ensure correct usage reporting.
- Adjusted metadata handling in CLIProxyAPI executors to address alias integration.

internal/runtime/executor/helps/usage_helpers.go

@@ -18,6 +18,7 @@ import (
 type UsageReporter struct {
 	provider    string
 	model       string
+	alias       string
 	authID      string
 	authIndex   string
 	authType    string
@@ -29,9 +30,14 @@ type UsageReporter struct {
 
 func NewUsageReporter(ctx context.Context, provider, model string, auth *cliproxyauth.Auth) *UsageReporter {
 	apiKey := APIKeyFromContext(ctx)
+	alias := usage.RequestedModelAliasFromContext(ctx)
+	if alias == "" {
+		alias = model
+	}
 	reporter := &UsageReporter{
 		provider:    provider,
 		model:       model,
+		alias:       strings.TrimSpace(alias),
 		requestedAt: time.Now(),
 		apiKey:      apiKey,
 		source:      resolveUsageSource(auth, apiKey),
@@ -139,6 +145,7 @@ func (r *UsageReporter) buildRecordForModel(model string, detail usage.Detail, f
 	return usage.Record{
 		Provider:    r.provider,
 		Model:       model,
+		Alias:       r.alias,
 		Source:      r.source,
 		APIKey:      r.apiKey,
 		AuthID:      r.authID,