cmake: declare version and policy requirements once at the top level (#808)

Each backend subdirectory (libusb, linux, mac, netbsd) called
cmake_minimum_required() with its own version range. That call resets
the CMake policy stack to the range's upper bound, discarding policies
introduced later. When hidapi is built as a CMake subproject (e.g. the
Meson cmake.subproject path), a modern CMake then emits dev warnings
for CMP0156/CMP0181/CMP0200 right after each backend's call.

The backends have no project() of their own and are never configured
standalone, so their cmake_minimum_required() calls served no purpose
beyond resetting policies. Remove them; the backends now inherit the
single policy baseline from the top-level CMakeLists.txt, matching what
windows/CMakeLists.txt already did.

Raise the top-level range to 3.6.3...4.3: 3.6.3 is the real floor (it
was already required by the linux/libusb/netbsd backends), and the 4.3
upper bound sets every current policy to NEW.

hidtest keeps its own cmake_minimum_required() because it is also built
as a standalone project; its upper bound is raised to 4.3 so it behaves
identically whether built standalone or as a subdirectory.

Assisted-by: Claude:claude-opus-4.7

Author: Copilot

CMakeLists.txt

@@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 3.1.3...3.25 FATAL_ERROR)
+cmake_minimum_required(VERSION 3.6.3...4.3 FATAL_ERROR)
 
 if(NOT CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR)
     add_subdirectory(src)

hidtest/CMakeLists.txt

@@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 3.1.3...3.25 FATAL_ERROR)
+cmake_minimum_required(VERSION 3.1.3...4.3 FATAL_ERROR)
 project(hidtest C)
 
 if(CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR)

libusb/CMakeLists.txt

@@ -1,5 +1,3 @@
-cmake_minimum_required(VERSION 3.6.3...3.25 FATAL_ERROR)
-
 list(APPEND HIDAPI_PUBLIC_HEADERS "hidapi_libusb.h")
 
 add_library(hidapi_libusb

linux/CMakeLists.txt

@@ -1,5 +1,3 @@
-cmake_minimum_required(VERSION 3.6.3...3.25 FATAL_ERROR)
-
 add_library(hidapi_hidraw
     ${HIDAPI_PUBLIC_HEADERS}
     hid.c

mac/CMakeLists.txt

@@ -1,5 +1,3 @@
-cmake_minimum_required(VERSION 3.4.3...3.25 FATAL_ERROR)
-
 list(APPEND HIDAPI_PUBLIC_HEADERS "hidapi_darwin.h")
 
 add_library(hidapi_darwin

netbsd/CMakeLists.txt

@@ -1,5 +1,3 @@
-cmake_minimum_required(VERSION 3.6.3...3.25 FATAL_ERROR)
-
 add_library(hidapi_netbsd
     ${HIDAPI_PUBLIC_HEADERS}
     hid.c