Improve the performance using the hints by rubocop-performance and fasterer

rubocop-performance (see https://github.com/rubocop-hq/rubocop-performance ) says:

Offenses:

/usr/lib/ruby/2.7.0/rexml/attlistdecl.rb:45:7: C: Performance/InefficientHashSearch: Use #key? instead of #keys.include?.
      @pairs.keys.include? key
      ^^^^^^^^^^^^^^^^^^^^^^^^
/usr/lib/ruby/2.7.0/rexml/doctype.rb:201:7: C: Performance/RegexpMatch: Use match? instead of =~ when MatchData is not used.
      quoted_string =~ /^[\'\"].*[\'\"]$/ ?
      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
/usr/lib/ruby/2.7.0/rexml/element.rb:255:43: C: Performance/RegexpMatch: Use match? instead of =~ when MatchData is not used.
        prefix = "xmlns:#{prefix}" unless prefix =~ /^xmlns:/
                                          ^^^^^^^^^^^^^^^^^^^
/usr/lib/ruby/2.7.0/rexml/entity.rb:44:12: C: Performance/RegexpMatch: Use match? instead of =~ when MatchData is not used.
        if stream[2] =~ /SYSTEM|PUBLIC/
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
/usr/lib/ruby/2.7.0/rexml/node.rb:56:9: C: Performance/RedundantBlockCall: Use yield instead of block.call.
        block.call(node)
        ^^^^^^^^^^^^^^^^
/usr/lib/ruby/2.7.0/rexml/node.rb:65:24: C: Performance/RedundantBlockCall: Use yield instead of block.call.
        return node if block.call(node)
                       ^^^^^^^^^^^^^^^^
/usr/lib/ruby/2.7.0/rexml/parseexception.rb:32:67: C: Performance/StringReplacement: Use tr instead of gsub.
        err << @source.buffer[0..80].force_encoding("ASCII-8BIT").gsub(/\n/, ' ')
                                                                  ^^^^^^^^^^^^^^^
/usr/lib/ruby/2.7.0/rexml/parsers/baseparser.rb:476:25: C: Performance/RegexpMatch: Use match? instead of =~ when MatchData is not used.
        return false if /\AUTF-16\z/i =~ xml_declaration_encoding
                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
/usr/lib/ruby/2.7.0/rexml/parsers/pullparser.rb:73:29: C: Performance/RegexpMatch: Use match? instead of =~ when MatchData is not used.
            event[2] unless event[2] =~ /PUBLIC|SYSTEM/
                            ^^^^^^^^^^^^^^^^^^^^^^^^^^^
/usr/lib/ruby/2.7.0/rexml/parsers/treeparser.rb:81:54: C: Performance/RegexpMatch: Use match? instead of =~ when MatchData is not used.
              entities[ event[1] ] = event[2] unless event[2] =~ /PUBLIC|SYSTEM/
                                                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^
/usr/lib/ruby/2.7.0/rexml/parsers/xpathparser.rb:304:14: C: Performance/RegexpMatch: Use match? instead of !~ when MatchData is not used.
          if path !~ /^\s*\)/
             ^^^^^^^^^^^^^^^^
/usr/lib/ruby/2.7.0/rexml/parsers/xpathparser.rb:539:41: C: Performance/RegexpMatch: Use match? instead of =~ when MatchData is not used.
        rest = LocationPath(rest, n) if rest =~ /\A[\/\.\@\[\w*]/
                                        ^^^^^^^^^^^^^^^^^^^^^^^^^
/usr/lib/ruby/2.7.0/rexml/quickpath.rb:108:49: C: Performance/RegexpMatch: Use match? instead of =~ when MatchData is not used.
      matches = filter( elements.dup, rest ) if axe_name =~ /-or-self$/u
                                                ^^^^^^^^^^^^^^^^^^^^^^^^

49 files inspected, 13 offenses detected

fasterer (see https://github.com/DamirSvrtan/fasterer) says:

validation/relaxng.rb:416 Calling argumentless methods within blocks is slower than using symbol to proc.
validation/relaxng.rb:523 Calling argumentless methods within blocks is slower than using symbol to proc.

parsers/xpathparser.rb:602 For loop is slower than using each.

parsers/baseparser.rb:381 For loop is slower than using each.

formatters/default.rb:70 Calling argumentless methods within blocks is slower than using symbol to proc.

xpath_parser.rb:105 For loop is slower than using each.
xpath_parser.rb:120 For loop is slower than using each.
xpath_parser.rb:458 Enumerable#sort is slower than Enumerable#sort_by.
xpath_parser.rb:590 Using each_with_index is slower than while loop.

quickpath.rb:88 Calling argumentless methods within blocks is slower than using symbol to proc.
quickpath.rb:133 Calling argumentless methods within blocks is slower than using symbol to proc.
quickpath.rb:135 Calling argumentless methods within blocks is slower than using symbol to proc.
quickpath.rb:138 Calling argumentless methods within blocks is slower than using symbol to proc.

node.rb:54 Calling blocks with call is slower than yielding.
node.rb:63 Calling blocks with call is slower than yielding.

functions.rb:42 Calling argumentless methods within blocks is slower than using symbol to proc.

element.rb:1068 Hash#fetch with second argument is slower than Hash#fetch with block.
element.rb:1075 Hash#fetch with second argument is slower than Hash#fetch with block.
element.rb:1128 Hash#fetch with second argument is slower than Hash#fetch with block.
element.rb:1212 Hash#fetch with second argument is slower than Hash#fetch with block.
element.rb:1246 Calling argumentless methods within blocks is slower than using symbol to proc.

doctype.rb:283 Use attr_reader for reading ivars.

49 files inspected, 22 offenses detected

Start with the files and line locations listed in the rubocop-performance and fasterer reports, especially the parser, XPath, quickpath, node, element, and doctype files. Run both tools against the project and review each suggested change for behavior preservation. Done means the reported offenses are addressed and the existing checks still pass.