Various style fixes

Submitting some miscellaneous changes I had locally. A few allocs saved,
but mostly style fixes here, like simplifying known var/var equality
using `==` and so on. Nothing controversial, or so I'd like to think :)

Signed-off-by: Anders Eknert <anders.eknert@apple.com>

internal/compile/compile.go

@@ -148,7 +148,7 @@ func ShortsFromMappings(mappings map[string]any) Set[string] {
 // number of rules present on the compiler. It should be used only for
 // error messages.
 func FuzzyRuleNameMatchHint(comp *ast.Compiler, input string) string {
-	rules := comp.GetRules(ast.Ref{ast.DefaultRootDocument})
+	rules := comp.GetRules(ast.DefaultRootRef)
 	ruleNames := make([]string, 0, len(rules))
 	for _, rule := range rules {
 		if rule.Default {