Fix: Prevent request deauthorization when loading assets

[iberianpig]

Description

This PR fixes the problem described in Issue #613, where requests to the /assets/ directory caused the __profilin cookie to be deleted, which in turn deactivated the client-side profiler.

Changes Made

• Prevent Cookie Deletion:

  • Updated the handle_cookie method to stop cookie deletion for asset requests by using preserve_cookie: true. This keeps the profiler's state when loading assets.
  • The commit in this PR is based on the work done by @Blayr

• Skip Asset Requests:

  • Added Rack::MiniProfiler.config.skip_paths = ['/assets'] to ignore asset requests during profiling checks. This is important because requests to /assets can still happen even if Rails.config.public_file_server.enabled is false.
  • When an asset is not found, the config.assets.unknown_asset_fallback option allows fallback handling, which can lead to extra requests to /assets. These paths were not fully considered in the dynamic skip paths configuration.

• Rails Version Handling:

  • Updated the condition to check which asset server configuration to use for different Rails versions. For Rails 5.1.0 and later, the code checks both public_file_server.enabled and unknown_asset_fallback.

With these changes, the unwanted cookie deletion that caused the error ActionController::RoutingError (No route matches [POST] "/mini-profiler-resources/results") no longer happens.