perf(parser): memoize createTrie to avoid rebuilding tries per Tokenizer (#911)

The Tokenizer constructor calls createTrie(operators) and
createTrie(literalValues) on every instantiation, and liquidjs builds a
fresh Tokenizer per output/tag while parsing. On typical templates this
rebuilt the same prefix-tries dozens of times and showed up as a large
share of parse CPU in profiling.

Memoize createTrie with a module-level WeakMap keyed on the input object.
The inputs (operators, literalValues) are stable references and the trie
is only ever read afterward (via matchTrie), never mutated, so caching by
reference is behavior-preserving. WeakMap (not Map) lets short-lived,
per-instance operator objects and their tries be garbage collected.

src/parser/tokenizer.spec.ts

@@ -522,6 +522,14 @@ describe('Tokenizer', function () {
       expect(new Tokenizer('contains b').matchTrie(opTrie)).toBe(8)
     })
   })
+  describe('#createTrie()', function () {
+    it('should return the same trie for the same input', () => {
+      expect(createTrie(defaultOperators)).toBe(createTrie(defaultOperators))
+    })
+    it('should return distinct tries for distinct inputs', () => {
+      expect(createTrie({ foo: 1 })).not.toBe(createTrie({ foo: 1 }))
+    })
+  })
   describe('#readLiquidTagTokens', () => {
     it('should read newline terminated tokens', () => {
       const tokenizer = new Tokenizer('echo \'hello\'')