Merge bitcoin#31691: util: fix compiler warning about deprecated spac…

…e before _MiB

d3339a7 util: fix compiler warning about deprecated space before _MiB (Vasil Dimov)

Pull request description:

  ```
  src/util/byte_units.h:13:29: error: identifier '_MiB' preceded by whitespace in a literal operator declaration is deprecated [-Werror,-Wdeprecated-literal-operator]
     13 | constexpr size_t operator"" _MiB(unsigned long long mebibytes)
        |                  ~~~~~~~~~~~^~~~
        |                  operator""_MiB
  1 error generated.
  ```

  Clang 20.0.0

ACKs for top commit:
  maflcko:
    lgtm ACK d3339a7
  TheCharlatan:
    ACK d3339a7

Tree-SHA512: 534537eefae2b6a9cef1ba3aa9ef16c491c84c0e55fb827f4ea0bae7ab61a5cc266a71499a79da97a9e68953a2c7f9cd1864ddde41fda173c829ed2b7bd73a46

src/util/byte_units.h

@@ -10,7 +10,7 @@
 #include <stdexcept>
 
 //! Overflow-safe conversion of MiB to bytes.
-constexpr size_t operator"" _MiB(unsigned long long mebibytes)
+constexpr size_t operator""_MiB(unsigned long long mebibytes)
 {
     auto bytes{CheckedLeftShift(mebibytes, 20)};
     if (!bytes || *bytes > std::numeric_limits<size_t>::max()) {