prefer caller_locations and Thread::Backtrace::Location methods

Mechanize has still been using `Kernel#caller` whose string
representation has changed enough in Ruby 3.4.0.dev to break how
deprecation messages were being handrolled.

Replace all uses of `caller` with `caller_locations` which is both
faster and returns an object with some nice methods we can use to
isolate the method, the file, and the line number.

This should get us green again on ruby-head.

lib/mechanize.rb

@@ -717,10 +717,10 @@ class << self
   # authentication.
 
   def auth user, password, domain = nil
-    caller.first =~ /(.*?):(\d+).*?$/
+    c = caller_locations(1,1).first
 
     warn <<-WARNING
-At #{$1} line #{$2}
+At #{c.absolute_path} line #{c.lineno}
 
 Use of #auth and #basic_auth are deprecated due to a security vulnerability.
 

lib/mechanize/cookie.rb

@@ -7,7 +7,7 @@ class Mechanize
   module CookieDeprecated
     def __deprecated__(to = nil)
       $VERBOSE or return
-      method = caller[0][/([^`]+)(?='$)/]
+      method = caller_locations(1,1).first.base_label
       to ||= method
       case self
       when Class
@@ -21,7 +21,7 @@ def __deprecated__(to = nil)
         this = '%s#%s' % [klass, method]
         that = 'HTTP::%s#%s' % [lname, to]
       end
-      warn '%s: The call of %s needs to be fixed to follow the new API (%s).' % [caller[1], this, that]
+      warn '%s: The call of %s needs to be fixed to follow the new API (%s).' % [caller_locations(2,1).first, this, that]
     end
     private :__deprecated__
   end

test/test_mechanize_http_agent.rb

@@ -29,7 +29,7 @@ def auth_realm uri, scheme, type
 
   def skip_if_jruby_zlib
     if RUBY_ENGINE == 'jruby'
-      meth = caller[0][/`(\w+)/, 1]
+      meth = caller_locations(1,1).first.base_label
       skip "#{meth}: skipped because how Zlib handles error is different in JRuby"
     end
   end

test/test_mechanize_page_link.rb

@@ -55,7 +55,7 @@ def util_page body = @body, res = @res
 
   def skip_if_nkf_dependency
     if RUBY_ENGINE == 'jruby'
-      meth = caller[0][/`(\w+)/, 1]
+      meth = caller_locations(1,1).first.base_label
       skip "#{meth}: skipped because this feature currently depends on NKF"
     end
   end