Squashed 'external/devlib/' changes from ff2268b7..fefdf29e

fefdf29e utils/asyn: Add memoize_method() decorator
0ea9c73e module/cpufreq: Fix async use_governor()
2c4b16f2 devlib: Use async Target API
18ab9f80 target: Expose Target(max_async=50) parameter
92f58e4e target: Enable async methods
bdf8b88a utils/async: Add new utils.async module
1da174a4 setup.py: Require Python >= 3.7
3c9804a4 setup.py: cleanup dependencies in setup.py
3fe105ff target: Make __getstate__ more future-proof
9bd76fd8 target: Fix Target.get_connection()'s busybox
ef9384d1 utils.misc: Make nullcontext work with asyncio

git-subtree-dir: external/devlib
git-subtree-split: fefdf29ed83075a87363078c0b3bbf77e80c5fe3