refactor(regex): cache array conversion (#3152)

Author: hackwaly

internal/regex_engine/compile.mbt

@@ -31,5 +31,12 @@ pub fn compile(profile~ : Profile, ast : Pattern) -> Regex {
   let tc = TranslateContext::new(ctx, symbol_table)
   let (expr, pref) = translate(tc, ast)
   let expr = enforce_pref(tc.ctx, First, pref, expr)
-  Regex::new(profile, ctx, expr, tc.groups, symbol_table, symbol_repr)
+  Regex::new(
+    profile,
+    ctx,
+    expr,
+    ReadOnlyArray::from_array(tc.groups),
+    symbol_table,
+    symbol_repr,
+  )
 }

internal/regex_engine/regex.mbt

@@ -17,7 +17,7 @@ struct Regex {
   profile : Profile
   ctx : @automata.Context
   expr : Expr
-  groups : Array[String?]
+  groups : ReadOnlyArray[String?]
   symbol_table : &@symbol_map.Table
   symbol_repr : ReadOnlyArray[Rechar]
   start_states : Array[(Category, State)]
@@ -26,15 +26,15 @@ struct Regex {
 
 ///|
 pub fn Regex::group_names(self : Regex) -> ReadOnlyArray[String?] {
-  ReadOnlyArray::from_array(self.groups)
+  self.groups
 }
 
 ///|
 fn Regex::new(
   profile : Profile,
   ctx : @automata.Context,
   expr : Expr,
-  groups : Array[String?],
+  groups : ReadOnlyArray[String?],
   symbol_table : &@symbol_map.Table,
   symbol_repr : ReadOnlyArray[Rechar],
 ) -> Regex {