🔥 Remove SASL.initial_response?, SASL.done?

Since they haven't been in any release yet, `SASL.initial_response?` and
`SASL.done?` have been removed without deprecation.  The logic has been
moved directly into `Net::IMAP#authenticate` (for now).

Implementing `#initial_response?` is still optional.  But, to simplify
the tests, `#initial_response? => false` was added to all of the
deprecated SASL mechanisms.

lib/net/imap.rb

@@ -1251,7 +1251,8 @@ def authenticate(mechanism, *creds, sasl_ir: true, **props, &callback)
       authenticator = SASL.authenticator(mechanism, *creds, **props, &callback)
       cmdargs = ["AUTHENTICATE", mechanism]
       if sasl_ir && capable?("SASL-IR") && auth_capable?(mechanism) &&
-          SASL.initial_response?(authenticator)
+          authenticator.respond_to?(:initial_response?) &&
+          authenticator.initial_response?
         response = authenticator.process(nil)
         cmdargs << (response.empty? ? "=" : [response].pack("m0"))
       end
@@ -1263,7 +1264,7 @@ def authenticate(mechanism, *creds, sasl_ir: true, **props, &callback)
           put_string(response + CRLF)
         end
       end
-      unless SASL.done?(authenticator)
+      if authenticator.respond_to?(:done?) && !authenticator.done?
         logout!
         raise SASL::AuthenticationFailed, "authentication ended prematurely"
       end

lib/net/imap/sasl.rb

@@ -158,24 +158,6 @@ def saslprep(string, **opts)
         Net::IMAP::StringPrep::SASLprep.saslprep(string, **opts)
       end
 
-      # Returns whether +authenticator+ is client-first and supports sending an
-      # "initial response".
-      def initial_response?(authenticator)
-        authenticator.respond_to?(:initial_response?) &&
-          authenticator.initial_response?
-      end
-
-      # Returns whether +authenticator+ considers the authentication exchange to
-      # be complete.
-      #
-      # The authentication should not succeed if this returns false, but
-      # returning true does *not* indicate success.  Authentication succeeds
-      # when this method returns true and the server responds with a
-      # protocol-specific success.
-      def done?(authenticator)
-        !authenticator.respond_to?(:done?) || authenticator.done?
-      end
-
     end
   end
 end

lib/net/imap/sasl/cram_md5_authenticator.rb

@@ -24,6 +24,8 @@ def initialize(user, password, warn_deprecation: true, **_ignored)
     @done = false
   end
 
+  def initial_response?; false end
+
   def process(challenge)
     digest = hmac_md5(challenge, @password)
     return @user + " " + digest

lib/net/imap/sasl/digest_md5_authenticator.rb

@@ -73,6 +73,8 @@ def initialize(user = nil, pass = nil, authz = nil,
     @nc, @stage = {}, STAGE_ONE
   end
 
+  def initial_response?; false end
+
   # Responds to server challenge in two stages.
   def process(challenge)
     case @stage

lib/net/imap/sasl/login_authenticator.rb

@@ -32,6 +32,8 @@ def initialize(user, password, warn_deprecation: true, **_ignored)
     @state = STATE_USER
   end
 
+  def initial_response?; false end
+
   def process(data)
     case @state
     when STATE_USER

test/net/imap/test_imap_authenticators.rb

@@ -41,7 +41,6 @@ def test_plain_authenticator_matches_mechanism
 
   def test_plain_supports_initial_response
     assert plain("foo", "bar").initial_response?
-    assert Net::IMAP::SASL.initial_response?(plain("foo", "bar"))
   end
 
   def test_plain_response
@@ -194,7 +193,6 @@ def test_xoauth2_kwargs
 
   def test_xoauth2_supports_initial_response
     assert xoauth2("foo", "bar").initial_response?
-    assert Net::IMAP::SASL.initial_response?(xoauth2("foo", "bar"))
   end
 
   # ----------------------
@@ -276,7 +274,7 @@ def test_login_authenticator_matches_mechanism
   end
 
   def test_login_does_not_support_initial_response
-    refute Net::IMAP::SASL.initial_response?(login("foo", "bar"))
+    refute login("foo", "bar").initial_response?
   end
 
   def test_login_authenticator_deprecated
@@ -306,7 +304,7 @@ def test_cram_md5_authenticator_matches_mechanism
   end
 
   def test_cram_md5_does_not_support_initial_response
-    refute Net::IMAP::SASL.initial_response?(cram_md5("foo", "bar"))
+    refute cram_md5("foo", "bar").initial_response?
   end
 
   def test_cram_md5_authenticator_deprecated
@@ -343,7 +341,7 @@ def test_digest_md5_authenticator_deprecated
   end
 
   def test_digest_md5_does_not_support_initial_response
-    refute Net::IMAP::SASL.initial_response?(digest_md5("foo", "bar"))
+    refute digest_md5("foo", "bar").initial_response?
   end
 
   def test_digest_md5_authenticator