fix: move non-fatal error to helpers (#167)

- Bug
## What does this PR do?

A quick fix PR to move `NonFatalErr` to helpers.go instead of
process.go.
This makes sure that `NonFatalErr` compiles for all OS'.
## Why is it important?

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## Related issues

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- Closes #123
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-

---------

Co-authored-by: Anderson Queiroz <[email protected]>

metric/system/process/helpers.go

@@ -99,6 +99,33 @@ func GetProcCPUPercentage(s0, s1 ProcState) ProcState {
 
 }
 
+// NonFatalErr indicates an error occurred during metrics
+// collection, however the metrics already
+// gathered and returned are still valid.
+// This error can be safely ignored, this will result
+// in having partial metrics for a process rather than
+// no metrics at all.
+//
+// It was introduced to allow for partial metrics collection
+// on privileged process on Windows.
+type NonFatalErr struct {
+	Err error
+}
+
+func (c NonFatalErr) Error() string {
+	return "Not enough privileges to fetch information: " + c.Err.Error()
+}
+
+func (c NonFatalErr) Is(other error) bool {
+	_, is := other.(NonFatalErr)
+	return is
+}
+
+func (c NonFatalErr) Unwrap() error {
+	return c.Err
+}
+
+// Wraps a NonFatalError around a generic error, if given error is non-fatal in nature
 func toNonFatal(err error) error {
 	if err == nil {
 		return nil

metric/system/process/process.go

@@ -218,32 +218,6 @@ func (procStats *Stats) pidIter(pid int, procMap ProcsMap, proclist []ProcState)
 	return procMap, proclist, nonFatalErr
 }
 
-// NonFatalErr is returned when there was an error
-// collecting metrics, however the metrics already
-// gathered and returned are still valid.
-// This error can be safely ignored, this will result
-// in having partial metrics for a process rather than
-// no metrics at all.
-//
-// It was introduced to allow for partial metrics collection
-// on privileged process on Windows.
-type NonFatalErr struct {
-	Err error
-}
-
-func (c NonFatalErr) Error() string {
-	return "Not enough privileges to fetch information: " + c.Err.Error()
-}
-
-func (c NonFatalErr) Is(other error) bool {
-	_, is := other.(NonFatalErr)
-	return is
-}
-
-func (c NonFatalErr) Unwrap() error {
-	return c.Err
-}
-
 // pidFill is an entrypoint used by OS-specific code to fill out a pid.
 // This in turn calls various OS-specific code to fill out the various bits of PID data
 // This is done to minimize the code duplication between different OS implementations