livecheck: support trailing comments in watchlist

I ran `brew livecheck` today to check the packages in my watchlist
and realized that it wasn't checking one package because I had added
a trailing comment after the name (and `package # Comment` isn't a
valid package name). I thought we had added support for trailing
comments when we originally added comment support years back but I
must have been mistaken.

This adds support for trailing comments in livecheck watchlist files
as part of refactoring the watchlist line parsing logic to only use
one pass (instead of multiple `#map` and `#reject` calls). This
maintains the existing behavior, where blank lines and lines starting
with `#` are skipped, but does so in a more flexible manner. For
example, the existing logic wouldn't skip a comment line that has one
or more spaces before the `#` character but this new logic will
correctly skip it.

Library/Homebrew/dev-cmd/livecheck.rb

@@ -78,9 +78,15 @@ module Homebrew
             formulae + casks
           elsif File.exist?(watchlist_path)
             begin
+              # This removes blank lines, comment lines, and trailing comments
               names = Pathname.new(watchlist_path).read.lines
-                              .reject { |line| line.start_with?("#") || line.blank? }
-                              .map(&:strip)
+                              .filter_map do |line|
+                                comment_index = line.index("#")
+                                next if comment_index&.zero?
+
+                                line = line[0...comment_index] if comment_index
+                                line&.strip.presence
+                              end
 
               named_args = CLI::NamedArgs.new(*names, parent: args)
               named_args.to_formulae_and_casks(ignore_unavailable: true)