mini_dump: Address review feedback

Uses fmt::print as opposed to std::fprintf. Adds a missing return.
static's a single-use function. Initializes structs as opposed to
std::memset where possible. Fixes CMake linkage.

Co-authored-by: Lioncash <mathew1800@gmail.com>

mini_dump: Use a namespace

Co-authored-by: Lioncash <mathew1800@gmail.com>