Refactor codebase, introduce relaymode package, update constants and improve consistency

- Refactor constant definitions and organization
- Clean up package level variables and functions
- Introduce new `relaymode` and `apitype` packages for constant definitions
- Refactor and simplify code in several packages including `openai`, `relay/channel/baidu`, `relay/util`, `relay/controller`, `relay/channeltype`
- Add helper functions in `relay/channeltype` package to convert channel type constants to corresponding API type constants
- Remove deprecated functions such as `ResponseText2Usage` from `relay/channel/openai/helper.go`
- Modify code in `relay/util/validation.go` and related files to use new `validator.ValidateTextRequest` function
- Rename `util` package to `relaymode` and update related imports in several packages

common/network/ip_test.go

@@ -0,0 +1,19 @@
+package network
+
+import (
+	"context"
+	"testing"
+
+	. "github.com/smartystreets/goconvey/convey"
+)
+
+func TestIsIpInSubnet(t *testing.T) {
+	ctx := context.Background()
+	ip1 := "192.168.0.5"
+	ip2 := "125.216.250.89"
+	subnet := "192.168.0.0/24"
+	Convey("TestIsIpInSubnet", t, func() {
+		So(isIpInSubnet(ctx, ip1, subnet), ShouldBeTrue)
+		So(isIpInSubnet(ctx, ip2, subnet), ShouldBeFalse)
+	})
+}