tap: cache more things at the Tap level

I added two new methods to cache both installed and all taps.
All taps includes core taps no matter if they're installed locally
since they're always provided by the API anyway.

This makes it easier to cache `Tap.each` while making the code
easier to reason about. It also will be useful because we'll
be able to avoid the `Tap.select(&:installed?` pattern that has
recently invaded the codebase.

Note: I also stopped clearing all tap instance caches before
tests. Running `Tap.each` would cache existing taps which would
lead to unexpected behavior since the only existing tap before
each test is the core tap. This is the only tap whose directory
is not cleaned up between tests so we just clear it's cache directly.
We also now clear all tap instances after tests as well regardless
of whether the API was used that time.

Library/Homebrew/tap.rb

@@ -402,6 +402,7 @@ class Tap
     end
 
     clear_cache
+    Tap.clear_cache
 
     $stderr.ohai "Tapping #{name}" unless quiet
     args =  %W[clone #{requested_remote} #{path}]
@@ -546,6 +547,7 @@ class Tap
 
     Commands.rebuild_commands_completion_list
     clear_cache
+    Tap.clear_cache
 
     return if !manual || !official?
 
@@ -931,27 +933,42 @@ class Tap
     other = Tap.fetch(other) if other.is_a?(String)
     other.is_a?(self.class) && name == other.name
   end
+  alias eql? ==
 
-  def self.each(&block)
-    return to_enum unless block
+  sig { returns(Integer) }
+  def hash
+    [self.class, name].hash
+  end
 
-    installed_taps = if TAP_DIRECTORY.directory?
-      TAP_DIRECTORY.subdirs
-                   .flat_map(&:subdirs)
-                   .map(&method(:from_path))
+  # All locally installed taps.
+  sig { returns(T::Array[Tap]) }
+  def self.installed
+    cache[:installed] ||= if TAP_DIRECTORY.directory?
+      TAP_DIRECTORY.subdirs.flat_map(&:subdirs).map(&method(:from_path))
     else
       []
     end
+  end
 
-    available_taps = if Homebrew::EnvConfig.no_install_from_api?
-      installed_taps
+  # All locally installed and core taps. Core taps might not be installed locally when using the API.
+  sig { returns(T::Array[Tap]) }
+  def self.all
+    cache[:all] ||= begin
+      core_taps = [
+        CoreTap.instance,
+        (CoreCaskTap.instance if OS.mac?), # rubocop:disable Homebrew/MoveToExtendOS
+      ].compact
+
+      installed | core_taps
+    end
+  end
+
+  def self.each(&block)
+    if Homebrew::EnvConfig.no_install_from_api?
+      installed.each(&block)
     else
-      default_taps = T.let([CoreTap.instance], T::Array[Tap])
-      default_taps << CoreCaskTap.instance if OS.mac? # rubocop:disable Homebrew/MoveToExtendOS
-      installed_taps + default_taps
-    end.sort_by(&:name).uniq
-
-    available_taps.each(&block)
+      all.each(&block)
+    end
   end
 
   # An array of all installed {Tap} names.

Library/Homebrew/test/spec_helper.rb

@@ -204,7 +204,7 @@ RSpec.configure do |config|
   config.around do |example|
     Homebrew.raise_deprecation_exceptions = true
 
-    Tap.each(&:clear_cache)
+    Tap.installed.each(&:clear_cache)
     Cachable::Registry.clear_all_caches
     FormulaInstaller.clear_attempted
     FormulaInstaller.clear_installed
@@ -244,9 +244,6 @@ RSpec.configure do |config|
     rescue SystemExit => e
       example.example.set_exception(e)
     ensure
-      # This depends on `HOMEBREW_NO_INSTALL_FROM_API`.
-      Tap.each(&:clear_cache)
-
       ENV.replace(@__env)
       Context.current = Context::ContextStruct.new
 
@@ -257,6 +254,7 @@ RSpec.configure do |config|
       @__stderr.close
       @__stdin.close
 
+      Tap.all.each(&:clear_cache)
       Cachable::Registry.clear_all_caches
 
       FileUtils.rm_rf [