* Update Nixpkgs base
* Clarify some comments
* Get rid of custom-packaged cxxbridge (it's now present in Nixpkgs as
cxx-rs)
* Add missing libraries (libdeflate, libxcrypt)
* Fix expected hash of the gdb patch
* Bump Python driver to 3.25.20-scylla
Fixes#12259
* Add some more useful stuff to the shell environment, so it actually
works for debugging & post-mortem analysis.
* Wrap ccache & distcc transparently (distcc will be used unless
NODISTCC is set to a non-empty value in the environment; ccache will
be used if CCACHE_DIR is not empty).
* Package the Scylla Python driver (instead of the C* one).
* Catch up to misc build/test requirements (including optional) by
requiring or custom-packaging: wasmtime 0.29.0, cxxbridge,
pytest-asyncio, liburing.
* Build statically-linked zstd in a saner and more idiomatic fashion.
* In pure builds (where sources lack Git metadata), derive
SCYLLA_RELEASE from source hash.
* Refactor things for more parameterization.
* Explicitly stub out installPhase (seeing that "nix build" succeeds
up to installPhase means we didn't miss any dependencies).
* Add flake support.
* Add copious comments.
Signed-off-by: Michael Livshin <michael.livshin@scylladb.com>