chore: Add named hooks for improved visibility and debugging (#261)

This commit introduces named hooks in place of anonymous functions
for the Fastify Helmet plugin. The changes include:

1. Renamed the first onRequest hook to 'helmetConfigureReply'
2. Renamed the second onRequest hook to 'helmetApplyHeaders'

These named hooks provide better visibility when inspecting routes
and improve the debugging experience. This change aligns the plugin
with other Fastify plugins like @fastify/cors that use named hooks.

The functionality remains unchanged; this is purely a developer
experience improvement.

index.js

@@ -33,7 +33,7 @@ async function fastifyHelmet (fastify, options) {
     }
   })
 
-  fastify.addHook('onRequest', async (request, reply) => {
+  fastify.addHook('onRequest', async function helmetConfigureReply (request, reply) {
     /* c8 ignore next */
     const { helmet: routeOptions } = request.routeOptions?.config || request.routeConfig
 
@@ -50,7 +50,7 @@ async function fastifyHelmet (fastify, options) {
     return replyDecorators(request, reply, globalConfiguration, enableCSPNonces)
   })
 
-  fastify.addHook('onRequest', (request, reply, next) => {
+  fastify.addHook('onRequest', function helmetApplyHeaders (request, reply, next) {
     /* c8 ignore next */
     const { helmet: routeOptions } = request.routeOptions?.config || request.routeConfig