Merge bitcoin/bitcoin#28486: test, bench: Initialize and terminate use of Winsock properly

fd4c6a10f2 test: Setup networking globally (Hennadii Stepanov)

Pull request description:

  On the master branch, when compiling without external signer support, the `bench_bitcoin.exe` does not initialize Winsock DLL that is required, for example, here: 459272d639/src/bench/addrman.cpp (L124)

  Moreover, Windows docs explicitly [state](https://learn.microsoft.com/en-us/windows/win32/api/winsock/nf-winsock-wsacleanup) that `WSAStartup` and `WSACleanup` must be balanced:
  > There must be a call to `WSACleanup` for each successful call to `WSAStartup`. Only the final `WSACleanup` function call performs the actual cleanup. The preceding calls simply decrement an internal reference count in the WS2_32.DLL.

  That is not the case for our unit tests because the `SetupNetworking()` call is a part of the `BasicTestingSetup` fixture and is invoked multiple times, while `~CNetCleanup()` is invoked once only, at the end of the test binary execution.

  This PR fixes Winsock DLL initialization and termination.

  More docs:
  - https://learn.microsoft.com/en-us/windows/win32/winsock/initializing-winsock
  - https://learn.microsoft.com/en-us/windows/win32/api/winsock/nf-winsock-wsastartup
  - https://learn.microsoft.com/en-us/windows/win32/api/winsock/nf-winsock-wsacleanup

  Fix https://github.com/bitcoin/bitcoin/issues/28940.

ACKs for top commit:
  maflcko:
    lgtm ACK fd4c6a10f2

Tree-SHA512: d360eaf776943f7f7a35ed5a5f9f3228d9e3d18eb824e5997cdc8eadddf466abe9f2da4910ee3bb86bf5411061e758259f7e1ec344f234ef7996f1bf8781dcda

src/common/system.h

@@ -17,7 +17,7 @@
 int64_t GetStartupTime();
 
 void SetupEnvironment();
-bool SetupNetworking();
+[[nodiscard]] bool SetupNetworking();
 #ifndef WIN32
 std::string ShellEscape(const std::string& arg);
 #endif