Build Route Regex once to reduce allocations

Right now every `match?` performed against the routes defined result
in a new Regex compiled for the exact same `@path`.

Since `@path` of the Route does not change on every request, we
pre-build it to avoid repeated allocations.

When testing this in release mode (against 0.10.2 [d1e3f0b]):

Before: 32408.48 req/s
After:  34862.07 req/s

src/kemal/route.cr

@@ -6,13 +6,14 @@ class Kemal::Route
   getter method
 
   def initialize(@method, @path, &@handler : Kemal::Context -> _)
+    @compiled_regex = pattern_to_regex(@path)
   end
 
   def match?(request)
     check_for_method_override!(request)
     return nil unless request.override_method == @method
     return true if request.path.not_nil!.includes?(':') && request.path.not_nil! == @path
-    request.path.not_nil!.match(pattern_to_regex(@path)) do |url_params|
+    request.path.not_nil!.match(@compiled_regex) do |url_params|
       request.url_params = url_params
       return true
     end