gh-136306: Add support for getting and setting SSL groups (#136307)

Add support for getting and setting groups used for key agreement.

* `ssl.SSLSocket.group()` returns the name of the group used
  for the key agreement of the current session establishment.
  This feature requires Python to be built with OpenSSL 3.2 or later.

* `ssl.SSLContext.get_groups()` returns the list of names of groups
  that are compatible with the TLS version of the current context.
  This feature requires Python to be built with OpenSSL 3.5 or later.

* `ssl.SSLContext.set_groups()` sets the groups allowed for key agreement
  for sockets created with this context. This feature is always supported.

Lib/ssl.py

@@ -931,6 +931,10 @@ class SSLObject:
         ssl_version, secret_bits)``."""
         return self._sslobj.cipher()
 
+    def group(self):
+        """Return the currently selected key agreement group name."""
+        return self._sslobj.group()
+
     def shared_ciphers(self):
         """Return a list of ciphers shared by the client during the handshake or
         None if this is not a valid server connection.
@@ -1210,6 +1214,14 @@ class SSLSocket(socket):
         else:
             return self._sslobj.cipher()
 
+    @_sslcopydoc
+    def group(self):
+        self._checkClosed()
+        if self._sslobj is None:
+            return None
+        else:
+            return self._sslobj.group()
+
     @_sslcopydoc
     def shared_ciphers(self):
         self._checkClosed()