[ruby/prism] Optimize ripper translator

Creating state classes is pretty expensive.
Since they are not modifiable, we can reuse them instead.

Benchmark script:
```rb
require "ripper"
require "prism"
require "benchmark/ips"

codes = Dir["**/*.rb"].map { File.read(it) }

Benchmark.ips do |x|
  x.config(time: 10)
  x.report("prism") { codes.each { Prism::Translation::Ripper.lex(it) } }
  x.report("ripper") { codes.each { Ripper.lex(it) } }

  x.compare!
end
```

Before:

```
ruby 4.0.0 (2025-12-25 revision ruby/prism@553f1675f3) +PRISM [x86_64-linux]
Warming up --------------------------------------
               prism     1.000 i/100ms
              ripper     1.000 i/100ms
Calculating -------------------------------------
               prism      0.293 (± 0.0%) i/s     (3.42 s/i) -      3.000 in  10.248348s
              ripper      0.633 (± 0.0%) i/s     (1.58 s/i) -      7.000 in  11.055687s

Comparison:
              ripper:        0.6 i/s
               prism:        0.3 i/s - 2.16x  slower
```

After

```
ruby 4.0.0 (2025-12-25 revision ruby/prism@553f1675f3) +PRISM [x86_64-linux]
Warming up --------------------------------------
               prism     1.000 i/100ms
              ripper     1.000 i/100ms
Calculating -------------------------------------
               prism      0.486 (± 0.0%) i/s     (2.06 s/i) -      5.000 in  10.280413s
              ripper      0.635 (± 0.0%) i/s     (1.58 s/i) -      7.000 in  11.027169s

Comparison:
              ripper:        0.6 i/s
               prism:        0.5 i/s - 1.31x  slower
```

ruby/prism@bdde16554c

Author: Earlopain

lib/prism/lex_compat.rb

@@ -667,7 +667,7 @@ def result
 
         event = RIPPER.fetch(token.type)
         value = token.value
-        lex_state = Translation::Ripper::Lexer::State.new(lex_state)
+        lex_state = Translation::Ripper::Lexer::State.cached(lex_state)
 
         token =
           case event
@@ -734,7 +734,7 @@ def result
                   counter += { on_embexpr_beg: -1, on_embexpr_end: 1 }[current_event] || 0
                 end
 
-                Translation::Ripper::Lexer::State.new(result_value[current_index][1])
+                Translation::Ripper::Lexer::State.cached(result_value[current_index][1])
               else
                 previous_state
               end

lib/prism/translation/ripper/lexer.rb

@@ -38,6 +38,13 @@ def |(i) self.class.new(to_int | i) end
           def allbits?(i) to_int.allbits?(i) end
           def anybits?(i) to_int.anybits?(i) end
           def nobits?(i) to_int.nobits?(i) end
+
+          # Instances are frozen and there are only a handful of them so we cache them here.
+          STATES = Hash.new { |h,k| h[k] = State.new(k) }
+
+          def self.cached(i)
+            STATES[i]
+          end
         end
 
         class Elem
@@ -47,7 +54,7 @@ def initialize(pos, event, tok, state, message = nil)
             @pos = pos
             @event = event
             @tok = tok
-            @state = State.new(state)
+            @state = State.cached(state)
             @message = message
           end