Micro-optimize Router#find_routes

`each_with_index` is unfortunately a noticeably slower
than `each`, especially when YJIT is enabled.

By incrementing the index ourselves we can squeeze a little
bit of performance in that hotspot.

Followup: rails#54504
Followup: rails#54491
Followup: rails#54505
Followup: rails#54515

Same benchmark as: rails#54491 (comment)

```
== index ==
ruby 3.4.1 (2024-12-25 revision 48d4efcb85) +YJIT +PRISM [arm64-darwin23]
Warming up --------------------------------------
               after    45.667k i/100ms
Calculating -------------------------------------
               after    480.940k (± 0.9%) i/s    (2.08 μs/i) -      2.420M in   5.032946s

Comparison:
              before:   458171.4 i/s
               after:   480939.8 i/s - 1.05x  faster

== show ==
ruby 3.4.1 (2024-12-25 revision 48d4efcb85) +YJIT +PRISM [arm64-darwin23]
Warming up --------------------------------------
               after    37.524k i/100ms
Calculating -------------------------------------
               after    374.480k (± 0.7%) i/s    (2.67 μs/i) -      1.876M in   5.010385s

Comparison:
              before:   358267.3 i/s
               after:   374479.9 i/s - 1.05x  faster

== show_nested ==
ruby 3.4.1 (2024-12-25 revision 48d4efcb85) +YJIT +PRISM [arm64-darwin23]
Warming up --------------------------------------
               after    35.187k i/100ms
Calculating -------------------------------------
               after    353.827k (± 0.7%) i/s    (2.83 μs/i) -      1.795M in   5.072038s

Comparison:
              before:   336299.6 i/s
               after:   353827.3 i/s - 1.05x  faster
```

Author: byroot

actionpack/lib/action_dispatch/journey/router.rb

@@ -118,15 +118,17 @@ def find_routes(req)
 
           routes.sort_by!(&:precedence)
 
-          routes.each { |r|
+          routes.each do |r|
             match_data = r.path.match(path_info)
             path_parameters = {}
-            match_data.names.each_with_index { |name, i|
-              val = match_data[i + 1]
+            index = 1
+            match_data.names.each do |name|
+              val = match_data[index]
               path_parameters[name.to_sym] = Utils.unescape_uri(val) if val
-            }
+              index += 1
+            end
             yield [match_data, path_parameters, r]
-          }
+          end
         end
 
         def match_head_routes(routes, req)