This commit adds a fast-path optimisation for when a BUILD_SLICE is
immediately followed by a LOAD/STORE_SUBSCR for a native type, to avoid
needing to allocate the slice on the heap.
In some cases (e.g. `a[1:3] = x`) this can result in no allocations at all.
We can't do this for instance types because the get/set/delattr
implementation may keep a reference to the slice.
Adds more tests to the basic slice tests to ensure that a stack-allocated
slice never makes it to Python, and also a heapalloc test that verifies
(when using bytecode) that assigning to a slice is no-alloc.
This work was funded through GitHub Sponsors.
Signed-off-by: Jim Mussared <jim.mussared@gmail.com>
Signed-off-by: Damien George <damien@micropython.org>
