Improve circular godoc comments flagged in review

Replace self-referential comments like 'ToSlice performs the ToSlice
operation' with meaningful descriptions of what the symbol actually does.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

internal/authflow/flow.go

@@ -119,7 +119,7 @@ type cfg struct {
 	token string
 }
 
-// ActiveToken performs the ActiveToken operation on cfg.
+// ActiveToken returns the active token and its source for the given hostname.
 func (c cfg) ActiveToken(hostname string) (string, string) {
 	return c.token, "oauth_token"
 }

internal/run/stub.go

@@ -12,7 +12,7 @@ const (
 	gitAuthRE = `-c credential(?:\..+)?\.helper= -c credential(?:\..+)?\.helper=!"[^"]+" auth git-credential `
 )
 
-// T defines the interface for t.
+// T is a minimal testing interface for use in command stubs.
 type T interface {
 	Helper()
 	Errorf(string, ...interface{})

pkg/set/string_set.go

@@ -67,12 +67,12 @@ func (s *stringSet) Contains(value string) bool {
 	return c
 }
 
-// Len returns the number of elements in stringSet.
+// Len returns the number of elements in the set.
 func (s *stringSet) Len() int {
 	return len(s.m)
 }
 
-// ToSlice performs the ToSlice operation on stringSet.
+// ToSlice returns the set elements as a slice.
 func (s *stringSet) ToSlice() []string {
 	return s.v
 }

test/helpers.go

@@ -17,7 +17,7 @@ func (c CmdOut) String() string {
 	return c.OutBuf.String()
 }
 
-// Stderr performs the Stderr operation on CmdOut.
+// Stderr returns the captured stderr output as a string.
 func (c CmdOut) Stderr() string {
 	return c.ErrBuf.String()
 }
@@ -44,7 +44,7 @@ func (s OutputStub) Run() error {
 	return nil
 }
 
-// T defines the interface for t.
+// T is a minimal testing interface for use in test helpers.
 type T interface {
 	Helper()
 	Errorf(string, ...interface{})