This change fixes a bug in which specifying 0 for timeout-related options (such as the `timeout` option of `Addrinfo.getaddrinfo`) incorrectly results in an infinite wait.

(This change overwrites https://github.com/ruby/ruby/pull/15626 .)

This change adds host information to the error messages shown when a timeout occurs while passing timeout options to `TCPSocket.new` or `Socket.tcp`, for improved usability.
(When the `fast_fallback option` is enabled, there may be multiple possible destinations, so the host name is shown instead of an IP address.)

As part of this change, the error messages in `Addrinfo.getaddrinfo` and `Addrinfo#connect_internal`, both of which are used by `Socket.tcp`, have also been improved in the same way.

Visual C++ 2008 (9.0):
- _MSC_VER: 1500
- MSVCRT_VERSION: 90

* [Feature #21347] Add `open_timeout` as an overall timeout option for `TCPSocket.new`

With this change, `TCPSocket.new` now accepts the `open_timeout` option.
This option raises an exception if the specified number of seconds has elapsed since the start of the method call,
even if the operation is still in the middle of name resolution or connection attempts.

The addition of this option follows the same intent as the previously merged change to `Socket.tcp`.
[Feature #21347](https://bugs.ruby-lang.org/issues/21347)
https://github.com/ruby/ruby/pull/13368

* Tidy up: Extract rsock_raise_user_specified_timeout()

* Added a note to the documentation of `Socket.tcp`

* Fix `rsock_init_inetsock` for `FAST_FALLBACK_INIT_INETSOCK_IMPL`

[Bug #21506] Fix timeout in Addrinfo.getaddrinfo to actually take effect

This change fixes an issue where the timeout option in `Addrinfo.getaddrinfo` was not functioning as expected.

It also addresses a related issue where specifying `fast_fallback: false` with `resolv_timeout` for `Socket.tcp` and`TCPSocket.new` would have no effect.

The timeout option was originally introduced in:
https://github.com/ruby/ruby/commit/6382f5cc91ac9e36776bc854632d9a1237250da7

However, the value was noy used in current implementation:
https://github.com/ruby/ruby/blob/3f0e0d5c8bf9046aee7f262a3f9a7524d51aaf3e/ext/socket/raddrinfo.c#L1282-1308

Therefore, even if a timeout is specified and the duration elapses during name resolution, nothing happens. This is clearly not the intended behavior.

`Addrinfo.getaddrinfo` has been made interruptible as of Feature #19965.
This change uses that feature to interrupt name resolution when the specified timeout period elapses, raising a user-specified timeout error.
The timeout can be specified in milliseconds.

The same issue affects `Socket.tcp` and `TCPSocket.new` when `resolv_timeout` is set along with `fast_fallback: false`.
`resolv_timeout` was introduced in the following commits:
https://github.com/ruby/ruby/commit/6382f5cc91ac9e36776bc854632d9a1237250da7
https://github.com/ruby/ruby/commit/511fe23fa2bdf1f17faa91e0558be47b5bb62b2a

The reason is that with `fast_fallback: false`, these methods internally call the same `rsock_getaddrinfo()` as `Addrinfo.getaddrinfo`.
This change addresses that as well.

otherwise, gcc 15 will complain:

> init.c:573:19: error: too many arguments to function ‘Rconnect’; expected 0, have 3
>   573 |     return (VALUE)Rconnect(arg->fd, arg->sockaddr, arg->len);
>       |                   ^~~~~~~~ ~~~~~~~
> In file included from init.c:11:
> rubysocket.h:294:5: note: declared here
>   294 | int Rconnect();
>       |     ^~~~~~~~

> sockssocket.c:33:9: error: too many arguments to function ‘SOCKSinit’; expected 0, have 1
>    33 |         SOCKSinit("ruby");
>       |         ^~~~~~~~~ ~~~~~~
> In file included from sockssocket.c:11:
> rubysocket.h:293:6: note: declared here
>   293 | void SOCKSinit();
>       |      ^~~~~~~~~

Signed-off-by: Z. Liu <zhixu.liu@gmail.com>

to avoid conflicts with other functions.
This was pointed out in https://github.com/ruby/ruby/pull/11653#discussion_r1837356617 , but it was not fixed at that time.

Wrap `do_fast_fallback_getaddrinfo` with `rb_thread_prevent_fork`

Referencing PR #10864,
wrap `do_fast_fallback_getaddrinfo` with `rb_thread_prevent_fork`
to avoid fork safety issues.

`do_fast_fallback_getaddrinfo` internally uses getaddrinfo(3),
leading to fork safety issues, as described in PR #10864.
This change ensures that `do_fast_fallback_getaddrinfo`
is guarded by `rb_thread_prevent_fork`,
preventing fork during its execution and avoiding related issues.

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)