feat: add priority for config loaders

[AkinoKaede]

related to #2620

V2Ray will try to use all config loaders if the config format isn't set. However, sometimes the config which written in other formats will be loaded as v4 format. A priority queue for loaders can solve this problem.

Priority Queue is not goroutine-safe, I think the priority queue will not be written after init().

[frankli0324]

I think this is not only over-engineered but also unable to fix the directory issue. the solution is simple as

diff --git a/main/commands/run.go b/main/commands/run.go
index 1e88b84..612d7af 100644
--- a/main/commands/run.go
+++ b/main/commands/run.go
@@ -119,9 +119,8 @@ func readConfDir(dirPath string, extension []string) cmdarg.Arg {
 	}
 	files := make(cmdarg.Arg, 0)
 	for _, f := range confs {
-		ext := filepath.Ext(f.Name())
 		for _, e := range extension {
-			if strings.EqualFold(e, ext) {
+			if strings.HasSuffix(f.Name(), e) {
 				files.Set(filepath.Join(dirPath, f.Name()))
 				break
 			}

[AkinoKaede]

I think this is not only over-engineered but also unable to fix the directory issue. the solution is simple as

diff --git a/main/commands/run.go b/main/commands/run.go
index 1e88b84..612d7af 100644
--- a/main/commands/run.go
+++ b/main/commands/run.go
@@ -119,9 +119,8 @@ func readConfDir(dirPath string, extension []string) cmdarg.Arg {
 	}
 	files := make(cmdarg.Arg, 0)
 	for _, f := range confs {
-		ext := filepath.Ext(f.Name())
 		for _, e := range extension {
-			if strings.EqualFold(e, ext) {
+			if strings.HasSuffix(f.Name(), e) {
 				files.Set(filepath.Join(dirPath, f.Name()))
 				break
 			}

The meaning of this modification solves the problem for users who do not know how to modify systemd files. I have received many related emails.

I think you can open an another PR.

[frankli0324]

then I believe a simple sort.Slice would suffice.