ANDROID: rust_binder: enforce that overflow in ptr_align is checked

Currently passing a very large integer to ptr_align can panic due to an
integer overflow. To fix this, change ptr_align to return an Option so
that the caller cannot forget to handle overflow when calling ptr_align.

Bug: 426634893
Change-Id: Iaf901fb2032d31b3054e023deaf227ecae0c81f2
Signed-off-by: Alice Ryhl <aliceryhl@google.com>