Regex string allocation (#1943)

Use Regexp instead of // for regex in router.rb for a more efficient string allocation.

Author: ericproulx

CHANGELOG.md

@@ -4,6 +4,7 @@
 
 * Your contribution here.
 * [#1944](https://github.com/ruby-grape/grape/pull/1944): Reduced attribute_translator string allocations - [@ericproulx](https://github.com/ericproulx).
+* [#1943](https://github.com/ruby-grape/grape/pull/1943): Reduce number of regex string allocations - [@ericproulx](https://github.com/ericproulx).
 * [#1942](https://github.com/ruby-grape/grape/pull/1942): Optimized retained memory methods - [@ericproulx](https://github.com/ericproulx).
 * [#1941](https://github.com/ruby-grape/grape/pull/1941): Frozen string literal - [@ericproulx](https://github.com/ericproulx).
 * [#1940](https://github.com/ruby-grape/grape/pull/1940): Get rid of a needless step in HashWithIndifferentAccess - [@dnesteryuk](https://github.com/dnesteryuk).

lib/grape/router.rb

@@ -41,7 +41,7 @@ def compile!
         routes = map[method]
         @optimized_map[method] = routes.map.with_index do |route, index|
           route.index = index
-          route.regexp = /(?<_#{index}>#{route.pattern.to_regexp})/
+          route.regexp = Regexp.new("(?<_#{index}>#{route.pattern.to_regexp})")
         end
         @optimized_map[method] = Regexp.union(@optimized_map[method])
       end
@@ -53,7 +53,7 @@ def append(route)
     end
 
     def associate_routes(pattern, **options)
-      regexp = /(?<_#{@neutral_map.length}>)#{pattern.to_regexp}/
+      regexp = Regexp.new("(?<_#{@neutral_map.length}>)#{pattern.to_regexp}")
       @neutral_map << Any.new(pattern, regexp, @neutral_map.length, **options)
     end