URI parser's RFC3986 regular expression has poor performance when there are two # characters, leading to ReDoS

Hello team, I hope you're doing well! The `URI` parser mishandles invalid URLs that have two `#` characters. It does correctly identify that they're invalid, but the regex performs very poorly and execution time grows much faster than the string length.

require 'benchmark'
require 'uri'

def parse(n)
  URI('https://example.com/dir/' + 'a' * n + '/##.jpg')
  rescue URI::InvalidURIError
  # Invalid URI because of the two #
end

n = 50000
Benchmark.bm(7) do |x|
  x.report('Base length') { parse(n) }
  x.report('Length x2  ') { parse(n * 2) } …