Rework how strategy constants are identified

Up to this point, we've had to rely on making `Strategy` constants
private to ensure that the only available constants are strategies.
With the current setup, the existence of a constant that's not a
strategy would break `Strategy#strategies` and
`Livecheck#livecheck_strategy_names`.

Instead, we can achieve the same goal by skipping over constants
that aren't a class. Other than saving us from having to make these
constants private, this is necessary to be able to create a
`Strategy` constant that can be used in all strategies.

Library/Homebrew/livecheck/livecheck.rb

@@ -56,9 +56,11 @@ module Homebrew
 
       # Cache demodulized strategy names, to avoid repeating this work
       @livecheck_strategy_names = {}
-      Strategy.constants.sort.each do |strategy_symbol|
-        strategy = Strategy.const_get(strategy_symbol)
-        @livecheck_strategy_names[strategy] = strategy.name.demodulize
+      Strategy.constants.sort.each do |const_symbol|
+        constant = Strategy.const_get(const_symbol)
+        next unless constant.is_a?(Class)
+
+        @livecheck_strategy_names[constant] = T.must(constant.name).demodulize
       end
       @livecheck_strategy_names.freeze
     end

Library/Homebrew/livecheck/strategy.rb

@@ -75,13 +75,6 @@ module Homebrew
       # In rare cases, this can also be a double newline (`\n\n`).
       HTTP_HEAD_BODY_SEPARATOR = "\r\n\r\n"
 
-      # The `#strategies` method expects `Strategy` constants to be strategies,
-      # so constants we create need to be private for this to work properly.
-      private_constant :DEFAULT_PRIORITY, :CURL_CONNECT_TIMEOUT, :CURL_MAX_TIME,
-                       :CURL_PROCESS_TIMEOUT, :DEFAULT_CURL_ARGS,
-                       :PAGE_HEADERS_CURL_ARGS, :PAGE_CONTENT_CURL_ARGS,
-                       :DEFAULT_CURL_OPTIONS, :HTTP_HEAD_BODY_SEPARATOR
-
       # Creates and/or returns a `@strategies` `Hash`, which maps a snake
       # case strategy name symbol (e.g. `:page_match`) to the associated
       # {Strategy}.
@@ -93,10 +86,12 @@ module Homebrew
         return @strategies if defined? @strategies
 
         @strategies = {}
-        constants.sort.each do |strategy_symbol|
-          key = strategy_symbol.to_s.underscore.to_sym
-          strategy = const_get(strategy_symbol)
-          @strategies[key] = strategy
+        Strategy.constants.sort.each do |const_symbol|
+          constant = Strategy.const_get(const_symbol)
+          next unless constant.is_a?(Class)
+
+          key = const_symbol.to_s.underscore.to_sym
+          @strategies[key] = constant
         end
         @strategies
       end