fix: Remove dependency on ActiveSupport core extensions from Grape instrumentation

[muripic]

Addresses #705

I checked if we are using any other core extensions apart from blank? using this as a reference: https://guides.rubyonrails.org/active_support_core_extensions.html

Also, instead of replacing directly with empty?, I added an extra check for nil?. We shouldn't get nil values here, but I added it as a safeguard in case there are any changes in the Grape gem that change this behaviour.

Another case that was covered by blank? but not by empty? is pure whitespace strings, but I decided not to add this since it would be very unlikely to have path with whitespace.

[arielvalentin]

Would safe navigation work?

Suggested change

	parts.reject { |p| p.nil? || p.empty? || p.eql?('/') }.join('/').prepend('/')
	parts.reject { |p| p&.empty? || p.eql?('/') }.join('/').prepend('/')

[muripic]

In this case, no, because p&.empty? returns nil if p is nil, which evaluates to false as a boolean.

3.1.3 :001 > p = nil
 => nil
3.1.3 :002 > p&.empty?
 => nil
3.1.3 :003 > p.nil? || p.empty? || p.eql?('/')
 => true
3.1.3 :004 > p&.empty? || p.eql?('/')
 => false

I guess there are refactor alternatives, but even though it is a bit verbose I thought it was quite readable like this. But of course I'm open to other suggestions 😃