[CAE-1072] Hitless Upgrades (#3447)

* feat(hitless): Introduce handlers for hitless upgrades

This commit includes all the work on hitless upgrades with the addition
of:

- Pubsub Pool
- Examples
- Refactor of push
- Refactor of pool (using atomics for most things)
- Introducing of hooks in pool


---------

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

logging/logging_test.go

@@ -0,0 +1,59 @@
+package logging
+
+import "testing"
+
+func TestLogLevel_String(t *testing.T) {
+	tests := []struct {
+		level    LogLevel
+		expected string
+	}{
+		{LogLevelError, "ERROR"},
+		{LogLevelWarn, "WARN"},
+		{LogLevelInfo, "INFO"},
+		{LogLevelDebug, "DEBUG"},
+		{LogLevel(99), "UNKNOWN"},
+	}
+
+	for _, test := range tests {
+		if got := test.level.String(); got != test.expected {
+			t.Errorf("LogLevel(%d).String() = %q, want %q", test.level, got, test.expected)
+		}
+	}
+}
+
+func TestLogLevel_IsValid(t *testing.T) {
+	tests := []struct {
+		level    LogLevel
+		expected bool
+	}{
+		{LogLevelError, true},
+		{LogLevelWarn, true},
+		{LogLevelInfo, true},
+		{LogLevelDebug, true},
+		{LogLevel(-1), false},
+		{LogLevel(4), false},
+		{LogLevel(99), false},
+	}
+
+	for _, test := range tests {
+		if got := test.level.IsValid(); got != test.expected {
+			t.Errorf("LogLevel(%d).IsValid() = %v, want %v", test.level, got, test.expected)
+		}
+	}
+}
+
+func TestLogLevelConstants(t *testing.T) {
+	// Test that constants have expected values
+	if LogLevelError != 0 {
+		t.Errorf("LogLevelError = %d, want 0", LogLevelError)
+	}
+	if LogLevelWarn != 1 {
+		t.Errorf("LogLevelWarn = %d, want 1", LogLevelWarn)
+	}
+	if LogLevelInfo != 2 {
+		t.Errorf("LogLevelInfo = %d, want 2", LogLevelInfo)
+	}
+	if LogLevelDebug != 3 {
+		t.Errorf("LogLevelDebug = %d, want 3", LogLevelDebug)
+	}
+}