rpn: use clear() builtin instead of loop+delete

Replace the manual for-range-delete pattern with Go 1.21+ clear()
builtin in Variables.ClearVariables() and Constants.ClearConstants().
Also simplified ReloadBuiltInConstants() which used the same pattern.

clear() is cleaner, more idiomatic, and slightly faster for
clearing entire maps.

1 files changed, 1 insertions, 3 deletions

diff --git a/internal/rpn/variables.go b/internal/rpn/variables.go
index efc2a8d..7e6b209 100644
--- a/internal/rpn/variables.go
+++ b/internal/rpn/variables.go
@@ -159,9 +159,7 @@ func (v *Variables) ClearVariables() {
 	v.mu.Lock()
 	defer v.mu.Unlock()
 
-	for k := range v.variables {
-		delete(v.variables, k)
-	}
+	clear(v.variables)
 }
 
 // formatVariablesUnsafe returns a list of variable info without acquiring a lock.