fix: add packaging as install-time dependency for flash-attn build

The flash-attn package requires the 'packaging' module during its build
process, but doesn't declare it as a build dependency. Adding it as an
install-time dependency ensures it's available before the unsloth package
tries to build flash-attn.

Signed-off-by: localai-bot <localai-bot@users.noreply.github.com>

Author: localai-bot

backend/python/unsloth/requirements-install.txt

@@ -0,0 +1 @@
+packaging