chore(refactor): drop duplicated shutdown logics (#3589)

* chore(refactor): drop duplicated shutdown logics

- Handle locking in Shutdown and CheckModelIsLoaded in a more go-idiomatic way
- Drop duplicated code and re-organize shutdown code

Signed-off-by: Ettore Di Giacinto <mudler@localai.io>

* fix: drop leftover

Signed-off-by: Ettore Di Giacinto <mudler@localai.io>

* chore: improve logging and add missing locks

Signed-off-by: Ettore Di Giacinto <mudler@localai.io>

---------

Signed-off-by: Ettore Di Giacinto <mudler@localai.io>

pkg/model/filters.go

@@ -0,0 +1,17 @@
+package model
+
+import (
+	process "github.com/mudler/go-processmanager"
+)
+
+type GRPCProcessFilter = func(id string, p *process.Process) bool
+
+func all(_ string, _ *process.Process) bool {
+	return true
+}
+
+func allExcept(s string) GRPCProcessFilter {
+	return func(id string, p *process.Process) bool {
+		return id != s
+	}
+}