Add CPython 3.16-dev, switch 3.15-dev to maintenance branch (#3442)

3.15.0b1 released means we need 3.16 support

plugins/python-build/bin/python-build

@@ -2276,6 +2276,11 @@ build_package_verify_py315() {
   build_package_verify_py314 "$1" "${2:-3.15}"
 }
 
+# Post-install check for Python 3.16.x
+build_package_verify_py316() {
+  build_package_verify_py315 "$1" "${2:-3.16}"
+}
+
 # Post-install check for Python 3.x rolling release scripts
 # XXX: Will need splitting into project-specific ones if there emerge
 # multiple rolling-release scripts with different checks needed

plugins/python-build/share/python-build/3.15-dev

@@ -5,4 +5,4 @@ export PYTHON_BUILD_TCLTK_USE_PKGCONFIG=1
 export PYTHON_BUILD_CONFIGURE_WITH_DSYMUTIL=1
 install_package "openssl-3.6.0" "https://github.com/openssl/openssl/releases/download/openssl-3.6.0/openssl-3.6.0.tar.gz#b6a5f44b7eb69e3fa35dbf15524405b44837a481d43d81daddde3ff21fcbb8e9" mac_openssl --if has_broken_mac_openssl
 install_package "readline-8.3" "https://ftpmirror.gnu.org/readline/readline-8.3.tar.gz#fe5383204467828cd495ee8d1d3c037a7eba1389c22bc6a041f627976f9061cc" mac_readline --if has_broken_mac_readline
-install_git "Python-3.15-dev" "https://github.com/python/cpython" main standard verify_py315 copy_python_gdb ensurepip
+install_git "Python-3.15-dev" "https://github.com/python/cpython" 3.15 standard verify_py315 copy_python_gdb ensurepip

plugins/python-build/share/python-build/3.16-dev

@@ -0,0 +1,8 @@
+prefer_openssl3
+export PYTHON_BUILD_CONFIGURE_WITH_OPENSSL=1
+export PYTHON_BUILD_TCLTK_USE_PKGCONFIG=1
+export PYTHON_BUILD_TCLTK_USE_PKGCONFIG=1
+export PYTHON_BUILD_CONFIGURE_WITH_DSYMUTIL=1
+install_package "openssl-3.6.0" "https://github.com/openssl/openssl/releases/download/openssl-3.6.0/openssl-3.6.0.tar.gz#b6a5f44b7eb69e3fa35dbf15524405b44837a481d43d81daddde3ff21fcbb8e9" mac_openssl --if has_broken_mac_openssl
+install_package "readline-8.3" "https://ftpmirror.gnu.org/readline/readline-8.3.tar.gz#fe5383204467828cd495ee8d1d3c037a7eba1389c22bc6a041f627976f9061cc" mac_readline --if has_broken_mac_readline
+install_git "Python-3.16-dev" "https://github.com/python/cpython" main standard verify_py316 copy_python_gdb ensurepip

plugins/python-build/share/python-build/3.16t-dev

@@ -0,0 +1,2 @@
+export PYTHON_BUILD_FREE_THREADING=1
+source "$(dirname "${BASH_SOURCE[0]}")"/3.16-dev