Improve APIs for Globally Enabling/Disabling fast_fallback in Socket (#12257)

This change includes the following updates:
- Added an environment variable `RUBY_TCP_NO_FAST_FALLBACK` to control enabling/disabling fast_fallback
- Updated documentation and man pages
- Revised the implementation of Socket.tcp_fast_fallback= and Socket.tcp_fast_fallback, which previously performed dynamic name resolution of constants and variables. As a result, the following performance improvements were achieved:

(Case of 1000 executions of `TCPSocket.new` to the local host)

Rehearsal -----------------------------------------
before   0.031462   0.147946   0.179408 (  0.249279)
after    0.031164   0.146839   0.178003 (  0.346935)
-------------------------------- total: 0.178003sec

            user     system      total        real
before   0.027584   0.138712   0.166296 (  0.233356)
after    0.025953   0.127608   0.153561 (  0.237971)

man/ruby.1

@@ -776,6 +776,17 @@ a program (or script) that is to be executed.
 .Pp
 The pipe template is split on spaces into an argument list before the
 template parameters are expanded.
+.Sh MISC ENVIRONMENT
+.Pp
+.Bl -hang -compact -width "RUBY_TCP_NO_FAST_FALLBACK"
+.It Ev RUBY_TCP_NO_FAST_FALLBACK
+If set to
+.Li 1 ,
+disables the fast fallback feature by default in TCPSocket.new and Socket.tcp.
+When set to
+.Li 0
+or left unset, the fast fallback feature is enabled.
+Introduced in Ruby 3.4, default: unset.
 .Sh SEE ALSO
 .Bl -hang -compact -width "https://www.ruby-toolbox.com/"
 .It Lk https://www.ruby-lang.org/